@article{thompson_zhu_hall_house_ranjan_burr_he_owens_smart_2011, title={C/EBP alpha Expression Is Downregulated in Human Nonmelanoma Skin Cancers and Inactivation of C/EBP alpha Confers Susceptibility to UVB-Induced Skin Squamous Cell Carcinomas}, volume={131}, ISSN={["0022-202X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-79956039252&partnerID=MN8TOARS}, DOI={10.1038/jid.2011.31}, abstractNote={Human epidermis is routinely subjected to DNA damage induced by UVB solar radiation. Cell culture studies have revealed an unexpected role for C/EBPα (CCAAT/enhancer-binding protein-α) in the DNA damage response network, where C/EBPα is induced following UVB DNA damage, regulates the G<sub>1</sub> checkpoint, and diminished or ablated expression of C/EBPα results in G<sub>1</sub> checkpoint failure. In the current study we observed that C/EBPα is induced in normal human epidermal keratinocytes and in the epidermis of human subjects exposed to UVB radiation. The analysis of human skin precancerous and cancerous lesions (47 cases) for C/EBPα expression was conducted. Actinic keratoses, a precancerous benign skin growth and precursor to squamous cell carcinoma (SCC), expressed levels of C/EBPα similar to normal epidermis. Strikingly, all invasive SCCs no longer expressed detectable levels of C/EBPα. To determine the significance of C/EBPα in UVB-induced skin cancer, SKH-1 mice lacking epidermal C/EBPα (CKOα) were exposed to UVB. CKOα mice were highly susceptible to UVB-induced SCCs and exhibited accelerated tumor progression. CKOα mice displayed keratinocyte cell cycle checkpoint failure <i>in vivo</i> in response to UVB that was characterized by abnormal entry of keratinocytes into S phase. Our results demonstrate that C/EBPα is silenced in human SCC and loss of C/EBPα confers susceptibility to UVB-induced skin SCCs involving defective cell cycle arrest in response to UVB.}, number={6}, journal={JOURNAL OF INVESTIGATIVE DERMATOLOGY}, author={Thompson, Elizabeth A. and Zhu, Songyun and Hall, Jonathan R. and House, John S. and Ranjan, Rakesh and Burr, Jeanne A. and He, Yu-Ying and Owens, David M. and Smart, Robert C.}, year={2011}, month={Jun}, pages={1339–1346} }
 @article{house_zhu_ranjan_linder_smart_2010, title={C/EBP alpha and C/EBP beta Are Required for Sebocyte Differentiation and Stratified Squamous Differentiation in Adult Mouse Skin}, volume={5}, ISSN={["1932-6203"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-79952118221&partnerID=MN8TOARS}, DOI={10.1371/journal.pone.0009837}, abstractNote={C/EBPα and C/EBPβ are bZIP transcription factors that are highly expressed in the interfollicular epidermis and sebaceous glands of skin and yet germ line deletion of either family member alone has only mild or no effect on keratinocyte biology and their role in sebocyte biology has never been examined. To address possible functional redundancies and reveal functional roles of C/EBPα and C/EBPβ in postnatal skin, mouse models were developed in which either family member could be acutely ablated alone or together in the epidermis and sebaceous glands of adult mice. Acute removal of either C/EBPα or C/EBPβ alone in adult mouse skin revealed modest to no discernable changes in epidermis or sebaceous glands. In contrast, co-ablation of C/EBPα and C/EBPβ in postnatal epidermis resulted in disruption of stratified squamous differentiation characterized by hyperproliferation of basal and suprabasal keratinocytes and a defective basal to spinous keratinocyte transition involving an expanded basal compartment and a diminished and delayed spinous compartment. Acute co-ablation of C/EBPα and C/EBPβ in sebaceous glands resulted in severe morphological defects, and sebocyte differentiation was blocked as determined by lack of sebum production and reduced expression of stearoyl-CoA desaturase (SCD3) and melanocortin 5 receptor (MC5R), two markers of terminal sebocyte differentiation. Specialized sebocytes of Meibomian glands and preputial glands were also affected. Our results indicate that in adult mouse skin, C/EBPα and C/EBPβ are critically involved in regulating sebocyte differentiation and epidermal homeostasis involving the basal to spinous keratinocyte transition and basal cell cycle withdrawal.}, number={3}, journal={PLOS ONE}, author={House, John S. and Zhu, Songyun and Ranjan, Rakesh and Linder, Keith and Smart, Robert C.}, year={2010}, month={Mar} }
 @article{ewing_zhu_zhu_house_smart_2008, title={C/EBP beta represses p53 to promote cell survival downstream of DNA damage independent of oncogenic Ras and p19(Arf)}, volume={15}, ISSN={["1476-5403"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-54049144611&partnerID=MN8TOARS}, DOI={10.1038/cdd.2008.105}, abstractNote={CCAAT/enhancer-binding protein-β (C/EBPβ) is a mediator of cell survival and tumorigenesis. When C/EBPβ−/− mice are treated with carcinogens that produce oncogenic Ras mutations in keratinocytes, they respond with abnormally elevated keratinocyte apoptosis and a block in skin tumorigenesis. Although this aberrant carcinogen-induced apoptosis results from abnormal upregulation of p53, it is not known whether upregulated p53 results from oncogenic Ras and its ability to induce p19Arf and/or activate DNA-damage response pathways or from direct carcinogen-induced DNA damage. We report that p19Arf is dramatically elevated in C/EBPβ−/− epidermis and that C/EBPβ represses a p19Arf promoter reporter. To determine whether p19Arf is responsible for the proapoptotic phenotype in C/EBPβ−/− mice, C/EBPβ−/−;p19Arf−/− mice were generated. C/EBPβ−/−;p19Arf−/− mice responded to carcinogen treatment with increased p53 and apoptosis, indicating p19Arf is not essential. To ascertain whether oncogenic Ras activation induces aberrant p53 and apoptosis in C/EBPβ−/− epidermis, we generated K14-ER:Ras;C/EBPβ−/− mice. Oncogenic Ras activation induced by 4-hydroxytamoxifen did not produce increased p53 or apoptosis. Finally, when C/EBPβ−/− mice were treated with differing types of DNA-damaging agents, including alkylating chemotherapeutic agents, they displayed aberrant levels of p53 and apoptosis. These results indicate that C/EBPβ represses p53 to promote cell survival downstream of DNA damage and suggest that inhibition of C/EBPβ may be a target for cancer cotherapy to increase the efficacy of alkylating chemotherapeutic agents.}, number={11}, journal={CELL DEATH AND DIFFERENTIATION}, author={Ewing, S. J. and Zhu, S. and Zhu, F. and House, J. S. and Smart, R. C.}, year={2008}, month={Nov}, pages={1734–1744} }
 @article{loomis_zhu_yoon_johnson_smart_2007, title={Genetic ablation of CCAAT/Enhancer binding protein alpha in epidermis reveals its role in suppression of epithelial tumorigenesis}, volume={67}, ISSN={["0008-5472"]}, DOI={10.1158/0008-5472.CAN-07-0139}, abstractNote={Abstract
               CCAAT/enhancer binding protein α (C/EBPα) is a basic leucine zipper transcription factor that inhibits cell cycle progression and regulates differentiation in various cell types. C/EBPα is inactivated by mutation in acute myeloid leukemia (AML) and is considered a human tumor suppressor in AML. Although C/EBPα mutations have not been observed in malignancies other than AML, greatly diminished expression of C/EBPα occurs in numerous human epithelial cancers including lung, liver, endometrial, skin, and breast, suggesting a possible tumor suppressor function. However, direct evidence for C/EBPα as an epithelial tumor suppressor is lacking due to the absence of C/EBPα mutations in epithelial tumors and the lethal effect of C/EBPα deletion in mouse model systems. To examine the function of C/EBPα in epithelial tumor development, an epidermal-specific C/EBPα knockout mouse was generated. The epidermal-specific C/EBPα knockout mice survived and displayed no detectable abnormalities in epidermal keratinocyte proliferation, differentiation, or apoptosis, showing that C/EBPα is dispensable for normal epidermal homeostasis. In spite of this, the epidermal-specific C/EBPα knockout mice were highly susceptible to skin tumor development involving oncogenic Ras. These mice displayed decreased tumor latency and striking increases in tumor incidence, multiplicity, growth rate, and the rate of malignant progression. Mice hemizygous for C/EBPα displayed an intermediate-enhanced tumor phenotype. Our results suggest that decreased expression of C/EBPα contributes to deregulation of tumor cell proliferation. C/EBPα had been proposed to block cell cycle progression through inhibition of E2F activity. We observed that C/EBPα blocked Ras-induced and epidermal growth factor–induced E2F activity in keratinocytes and also blocked Ras-induced cell transformation and cell cycle progression. Our study shows that C/EBPα is dispensable for epidermal homeostasis and provides genetic evidence that C/EBPα is a suppressor of epithelial tumorigenesis. [Cancer Res 2007;67(14):6768–76]}, number={14}, journal={CANCER RESEARCH}, author={Loomis, Kari D. and Zhu, Songyun and Yoon, Kyungsil and Johnson, Peter F. and Smart, Robert C.}, year={2007}, month={Jul}, pages={6768–6776} }
 @article{sterneck_zhu_ramirez_jorcano_smart_2006, title={Conditional ablation of C/EBP beta demonstrates its keratinocyte-specific requirement for cell survival and mouse skin tumorigenesis}, volume={25}, ISSN={["1476-5594"]}, DOI={10.1038/sj.onc.1209144}, abstractNote={The CCAAT/enhancer binding protein β (C/EBPβ) is implicated in the regulation of many different molecular and physiological processes. Mice with a germline deletion of C/EBPβ (C/EBPβ−/−) display phenotypes in a multitude of cell types and organ systems, including skin where C/EBPβ−/− mice exhibit increased apoptosis in epidermal keratinocytes in response to carcinogen treatment and are completely resistant to carcinogen-induced skin tumorigenesis. To determine the contribution of systemic versus cell autonomous functions of C/EBPβ to specific phenotypes, mice with a conditional ‘floxed’ C/EBPβ null allele were generated. Epidermal-specific deletion of C/EBPβ was achieved by Cre recombinase expression from a keratin 5 (K5) promoter. Similar to C/EBPβ−/− mice, K5-Cre;C/EBPβfl/fl mice were completely refractory to 7,12 dimethylbenz[a]anthracene (DMBA)-induced skin tumorigenesis and these mice displayed increased DMBA-induced apoptosis in epidermal keratinocytes compared to wild-type mice. In contrast, mice lacking the related gene, C/EBPδ, were not resistant to DMBA-induced skin tumorigenesis, indicating a unique role of C/EBPβ in skin tumor development. Our findings demonstrate that C/EBPβ exerts an essential, keratinocyte-intrinsic role in cell survival in response to carcinogen treatment and the elimination of C/EBPβ in keratinocytes is sufficient to confer complete resistance of the skin to chemical carcinogenesis.}, number={8}, journal={ONCOGENE}, author={Sterneck, E and Zhu, S and Ramirez, A and Jorcano, JL and Smart, RC}, year={2006}, month={Feb}, pages={1272–1276} }
 @article{shim_powers_ewing_zhu_smart_2005, title={Diminished expression of C/EBP alpha in skin carcinomas is linked to oncogenic Ras and reexpression of C/EBP alpha in carcinoma cells inhibits proliferation}, volume={65}, number={3}, journal={Cancer Research}, author={Shim, M. and Powers, K. L. and Ewing, S. J. and Zhu, S. and Smart, R. C.}, year={2005}, pages={861–867} }
 @article{shuman_sebastian_kaldis_copeland_zhu_smart_johnson_2004, title={Cell cycle-dependent phosphorylation of C/EBP beta mediates oncogenic cooperativity between C/EBP beta and H-Ras(V12)}, volume={24}, ISSN={["1098-5549"]}, DOI={10.1128/MCB.24.17.7380-7391.2004}, abstractNote={ABSTRACT CCAAT/enhancer binding protein β (C/EBPβ) is a widely expressed transcription factor whose activity is regulated by oncogenic Ha-RasV12 signaling. C/EBPβ is essential for the development of mouse skin tumors containing Ras mutations and can cooperate with RasV12 to transform NIH 3T3 cells. Here we have investigated Ras-induced phosphorylation of C/EBPβ in fibroblasts and report a novel proline-directed phosphoacceptor site at Ser64 within the transactivation domain. Ser64 phosphorylation was induced by activated Ras and Raf but was not blocked by chemical inhibitors of MEK1/2, phosphatidylinositol 3-kinase, JNK, or p38 mitogen-activated protein kinases. Ser64 was efficiently phosphorylated in vitro by the cyclin-dependent kinases Cdk2 and Cdc2. Thr189, previously identified as an ERK1/2 phosphorylation site that regulates C/EBPβ activity, was also a substrate for Cdk phosphorylation. Ser64 and Thr189 phosphorylation was low in serum-starved (G0) cells but was strongly increased in mid-G1 cells and in cells arrested in S or M phase. In addition, phosphorylation on both sites was blocked by treating cells with the Cdk inhibitor roscovitine. In contrast to wild-type C/EBPβ, which enhances transformation of NIH 3T3 cells, mutants bearing alanine substitutions at Ser64 and/or Thr189 inhibited RasV12-induced focus formation. Our findings support a role for C/EBPβ as a nuclear effector of Ras signaling and transformation, and they indicate that cell cycle-dependent phosphorylation of C/EBPβ on Ser64 and Thr189 is required to promote Ras-induced transformation of NIH 3T3 cells.}, number={17}, journal={MOLECULAR AND CELLULAR BIOLOGY}, author={Shuman, JD and Sebastian, T and Kaldis, P and Copeland, TD and Zhu, SY and Smart, RC and Johnson, PF}, year={2004}, month={Sep}, pages={7380–7391} }
 @article{zhu_yoon_sterneck_johnson_smart_2002, title={CCAAT/enhancer binding protein-beta is a mediator of keratinocyte survival and skin tumorigenesis involving oncogenic Ras signaling}, volume={99}, ISSN={["0027-8424"]}, DOI={10.1073/pnas.012437299}, abstractNote={The basic leucine zipper transcription factor CCAAT/enhancer binding protein-β (C/EBPβ) is expressed in many cell types, including keratinocytes. C/EBPβ activity can be increased by phosphorylation through pathways stimulated by oncogenic Ras, although the biological implications of Ras-C/EBPβ signaling are not currently understood. We report here thatC/EBPβ-nullizygous mice are completely refractory to skin tumor development induced by a variety of carcinogens and carcinogenesis protocols, including 7,12-dimethylbenz[a]anthracene-initiation/12-O-tetradecanoylphorbol 13-acetate promotion, that produce tumors containing oncogenicRasmutations. No significant differences in TPA-induced epidermal keratinocyte proliferation were observed inC/EBPβ-null versus wild-type mice. However, apoptosis was significantly elevated (17-fold) in the epidermal keratinocytes of 7,12-dimethylbenz[a]anthracene-treatedC/EBPβ-null mice compared with wild-type mice. In v-Ha-rastransgenic mice,C/EBPβ deficiency also led to greatly reduced skin tumor multiplicity and size, providing additional evidence for a tumorigenesis pathway linking Ras and C/EBPβ. Oncogenic Ras potently stimulated C/EBPβ to activate a C/EBP-responsive promoter-reporter in keratinocytes and mutating an ERK1/2 phosphorylation site (T188) in C/EBPβ abolished this Ras effect. Finally, we observed that C/EBPβ participates in oncogenic Ras-induced transformation of NIH 3T3 cells. These findings indicate that C/EBPβ has a critical role in Ras-mediated tumorigenesis and cell survival and implicate C/EBPβ as a target for tumor inhibition.}, number={1}, journal={PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA}, author={Zhu, SY and Yoon, K and Sterneck, E and Johnson, PF and Smart, RC}, year={2002}, month={Jan}, pages={207–212} }