C/EBP transcription factors in human squamous cell carcinoma: selective changes in expression of isoforms correlate with the neoplastic state.
The CCAAT/Enhancer Binding Proteins (C/EBPs) are a family of leucine-zipper transcription factors that regulate physiological processes such as energy metabolism, inflammation, cell cycle, and the development and differentiation of several tissues including skin. Recently, a role for C/EBPs in tumor cell proliferation and differentiation has been proposed, but the incomplete characterization in the literature of multiple translational isoforms of these proteins has made interpretation of these roles difficult. Therefore, we have carefully reexamined C/EBP isoform expression in human non-melanoma skin cancers. C/EBPα, C/EBPβ, and C/EBPδ were analyzed histologically in squamous cell carcinomas (SCC). The individual isoforms of C/EBPα and C/EBPβ were examined by immunofluorescent digital imaging, western blotting and DNA binding activity (electrophoretic mobility shift analysis). Expression of all C/EBP family proteins was decreased in SCC tumors. Suppression was greatest for C/EBPα, less for C/EBPβ, and least for C/EBPδ. Western analyses confirmed that C/EBPα p42 and p30 isoforms were decreased. For C/EBPβ, only the abundant full-length isoform (C/EBPβ-1, LAP*, 55 kD) was reduced, whereas the smaller isoforms, C/EBPβ-2 (LAP, 48 kD) and C/EBPβ-3 (LIP, 20 kD), which are predominantly nuclear, were significantly increased in well- and moderately-differentiated SCC (up to 14-fold for C/EBPβ-3). These elevations correlated with increases in PCNA, a marker of proliferation. Although C/EBPβ displayed increased post-translational modifications in SCC, phosphorylation of C/EBPβ-1 (Thr 235) was not altered. C/EBP-specific DNA binding activity in nuclear and whole-cell extracts of cultured cells and tumors was predominantly attributable to C/EBPβ. In summary, two short C/EBPβ isoforms, C/EBPβ-2 and C/EBPβ-3, represent strong candidate markers for epithelial skin malignancy, due to their preferential expression in carcinoma versus normal skin, and their strong correlation with tumor proliferation.
Department of Dermatology, Cleveland Clinic, Cleveland, Ohio, United States of America; Department of Biomedical Engineering, Cleveland Clinic, Cleveland, Ohio, United States of America.
Sanjay
S
Anand
Department of Dermatology, Cleveland Clinic, Cleveland, Ohio, United States of America.
John
J
Ebner
Department of Dermatology, Cleveland Clinic, Cleveland, Ohio, United States of America.
Christine B
CB
Warren
Department of Biomedical Engineering, Cleveland Clinic, Cleveland, Ohio, United States of America.
Manu S
MS
Raam
Department of Dermatology, Cleveland Clinic, Cleveland, Ohio, United States of America; Department of Anatomic Pathology, Cleveland Clinic, Cleveland, Ohio, United States of America.
Melissa
M
Piliang
Department of Dermatology, Cleveland Clinic, Cleveland, Ohio, United States of America; Department of Anatomic Pathology, Cleveland Clinic, Cleveland, Ohio, United States of America.
Steven D
SD
Billings
Department of Dermatology, Cleveland Clinic, Cleveland, Ohio, United States of America; Department of Biomedical Engineering, Cleveland Clinic, Cleveland, Ohio, United States of America; Wellman Center for Photomedicine, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, United States of America.
Edward V
EV
Maytin
D017398:Alternative Splicing; D001706:Biopsy; D022763:CCAAT-Enhancer-Binding Protein-alpha / Q000235:genetics / Q000378:metabolism; D022782:CCAAT-Enhancer-Binding Protein-beta / Q000235:genetics / Q000378:metabolism; D051743:CCAAT-Enhancer-Binding Protein-delta / Q000235:genetics / Q000378:metabolism; D022762:CCAAT-Enhancer-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D002294:Carcinoma, Squamous Cell / Q000235:genetics* / Q000473:pathology*; D045744:Cell Line, Tumor; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D009367:Neoplasm Staging; D010766:Phosphorylation; D059368:RNA Isoforms; D012878:Skin Neoplasms / Q000235:genetics / Q000378:metabolism
D022763:CCAAT-Enhancer-Binding Protein-alpha; D022782:CCAAT-Enhancer-Binding Protein-beta; D022762:CCAAT-Enhancer-Binding Proteins; D059368:RNA Isoforms; D051743:CCAAT-Enhancer-Binding Protein-delta