Tripartite motif containing 28 (Trim28) can regulate cell proliferation by bridging HDAC1/E2F interactions.
BACKGROUND
Trim28 appears up-regulated in many cancers.


RESULTS
In early stage lung tumors high Trim28 correlates with increased overall survival and Trim28 reduces cell proliferation in model lung cancer cell lines through E2F interactions.


CONCLUSIONS
Trim28 may have a tumor suppressing role in the early stages of lung cancer.


CONCLUSIONS
These results suggest a complex role for Trim28 in lung cancer. Trim28 is a poorly understood transcriptional co-factor with pleiotropic biological activities. Although Trim28 mRNA is found in many studies to be up-regulated in both lung and breast cancer tissues relative to normal adjacent tissue, we found that within a panel of early-stage lung adenocarcinomas high levels of Trim28 protein correlate with better overall survival. This surprising observation suggests that Trim 28 may have anti-proliferative activity within tumors. To test this hypothesis, we used shRNAi to generate Trim28-knockdown breast and lung cancer cell lines and found that Trim28 depletion led to increased cell proliferation. Likewise, overexpression of Trim28 led to decreased cell proliferation. Confocal microscopy indicated co-localization of E2F3 and E2F4 with Trim28 within the cell nucleus, and co-immunoprecipitation assays demonstrated that Trim28 can bind both E2F3 and E2F4. Trim28 overexpression inhibited the transcriptional activity of E2F3 and E2F4, whereas Trim28 deficiency enhanced their activity. Co-immunoprecipitations further indicated that Trim28 bridges an interaction between E2Fs 3 and 4 and HDAC1. Promoter-reporter assays demonstrated that the ability of HDAC1 to repress E2F3 and E2F4-driven transcription is dependent on Trim28. Trim28 depletion increased E2F3 and E2F4 DNA binding activity, as measured by chromatin-immunoprecipitation (ChIP) assays while simultaneously reducing HDAC1 binding. Finally, ChIP-ReChIP experiments demonstrated that Trim/E2F complexes exist on several E2F-regulated promoters. Taken together, these results suggest that Trim28 has anti-proliferative activity in lung cancers via repression of members of the E2F family that are critical for cell proliferation.
Molecular Oncology Program, H. Lee Moffitt Cancer Center and Research Institute, Tampa, FL 33612, USA.
Lu
L
Chen
Dung-Tsa
DT
Chen
Courtney
C
Kurtyka
Bhupendra
B
Rawal
William J
WJ
Fulp
Eric B
EB
Haura
W Douglas
WD
Cress
D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000503:physiopathology; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D004247:DNA / Q000235:genetics / Q000378:metabolism; D050699:E2F3 Transcription Factor / Q000235:genetics / Q000378:metabolism*; D050704:E2F4 Transcription Factor / Q000235:genetics / Q000378:metabolism*; D005260:Female; D056284:Histone Deacetylase 1 / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008175:Lung Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000503:physiopathology; D008297:Male; D011485:Protein Binding; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D000076183:Tripartite Motif-Containing Protein 28
D050699:E2F3 Transcription Factor; D050704:E2F4 Transcription Factor; D012097:Repressor Proteins; D004247:DNA; C101116:TRIM28 protein, human; D000076183:Tripartite Motif-Containing Protein 28; C110550:HDAC1 protein, human; D056284:Histone Deacetylase 1