Modulation of proliferation-specific and differentiation-specific markers in human keratinocytes by SMAD7.
We examined the potential role of SMAD7 in human epidermal keratinocyte differentiation. Overexpression of SMAD7 inhibited the activity of the proliferation-specific promoters for the keratin 14 and cdc2 genes and reduced the expression of the mRNA for the proliferation-specific genes cdc2 and E2F1. The ability of SMAD7 to suppress cdc2 promoter activity was lost in transformed keratinocyte cell lines and was mediated by a domain(s) located between aa 195-395 of SMAD7. This domain lies outside the domain required to inhibit TGFbeta1 signaling, suggesting that this activity is mediated by a novel functional domain(s). Examination of AP1, NFkappaB, serum response element, Gli, wnt, and E2F responsive reporters indicated that SMAD7 significantly suppressed the E2F responsive reporter and modestly increased AP1 activity in proliferating keratinocytes. These data suggest that SMAD7 may have a role in TGFbeta-independent signaling events in proliferating/undifferentiated keratinocytes. The effects of SMAD7 in differentiated keratinocytes indicated a more traditional role for SMAD7 as an inhibitor of TGFbeta action. SMAD7 was unable to initiate the expression of differentiation markers but was able to superinduce/derepress differentiation-specific markers and genes in differentiated keratinocytes. This latter role is consistent with the ability of SMAD7 to inhibit TGFbeta-mediated suppression of keratinocyte differentiation and suggest that the opposing actions of SMAD7 and TGFbeta may serve to modulate squamous differentiation.
Smith
Louise
L
Epithelial Pathobiology Group, Cancer Biology Programme, Centre for Immunology and Cancer Research, University of Queensland, Princess Alexandra Hospital, Brisbane, Queensland, Australia.
Dahler
Alison L
AL
Cavanagh
Lois L
LL
Popa
Claudia
C
Barnes
Liam M
LM
Serewko-Auret
Magdalena M M
MM
Fai Wong
C
C
Saunders
Nicholas A
NA
D000943:Antigens, Differentiation / Q000378:metabolism*; D015415:Biomarkers; D016203:CDC2 Protein Kinase / Q000235:genetics; D018797:Cell Cycle Proteins; D002454:Cell Differentiation / Q000235:genetics*; D002455:Cell Division / Q000235:genetics; D045744:Cell Line, Tumor; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D017930:Genes, Reporter / Q000235:genetics; D006801:Humans; D053547:Keratin-14; D015603:Keratinocytes / Q000166:cytology / Q000378:metabolism*; D007633:Keratins / Q000235:genetics; D011401:Promoter Regions, Genetic / Q000235:genetics; D017434:Protein Structure, Tertiary / Q000235:genetics; D012333:RNA, Messenger / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D051906:Smad7 Protein; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D018808:Transcription Factor AP-1 / Q000235:genetics; D014157:Transcription Factors / Q000235:genetics; D016212:Transforming Growth Factor beta / Q000378:metabolism*
D000943:Antigens, Differentiation; D015415:Biomarkers; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; C493753:E2F1 protein, human; C507540:KRT14 protein, human; D053547:Keratin-14; D012333:RNA, Messenger; D012097:Repressor Proteins; C497806:SMAD7 protein, human; D051906:Smad7 Protein; D015534:Trans-Activators; D018808:Transcription Factor AP-1; D014157:Transcription Factors; D016212:Transforming Growth Factor beta; D007633:Keratins; D016203:CDC2 Protein Kinase