In vitro, cellular immortalization and transformation define a model for multistep
carcinogenesis and current ongoing challenges include the identification of specific molecular events associated with steps along this oncogenic pathway. Here, using NIH3T3 cells, we identified transcriptionally related events associated with the expression of Polyomavirus
Large-T antigen (PyLT), a potent viral oncogene. We propose that a subset of these alterations in gene expression may be related to the early events that contribute to
carcinogenesis. The proposed
tumor suppressor
Necdin, known to be regulated by p53, was within a group of genes that was consistently upregulated in the presence of PyLT. While
Necdin is induced following p53 activation with different genotoxic stresses,
Necdin induction by PyLT did not involve p53 activation or the Rb-binding site of PyLT.
Necdin depletion by
shRNA conferred a proliferative advantage to NIH3T3 and PyLT-expressing NIH3T3 (NIHLT) cells. In contrast, our results demonstrate that although overexpression of
Necdin induced a growth arrest in NIH3T3 and NIHLT cells, a growing population rapidly emerged from these arrested cells. This population no longer showed significant proliferation defects despite high
Necdin expression. Moreover, we established that
Necdin is a negative regulator of p53-mediated growth arrest induced by
nutlin-3, suggesting that
Necdin upregulation could contribute to the bypass of a p53-response in p53 wild type
tumors. To support this, we characterized
Necdin expression in low malignant potential
ovarian cancer (LMP) where p53 mutations rarely occur. Elevated levels of
Necdin expression were observed in LMP when compared to aggressive serous
ovarian cancers. We propose that in some contexts, the constitutive expression of
Necdin could contribute to
cancer promotion by delaying appropriate p53 responses and potentially promote
genomic instability.