Evidence that RASSF1C stimulation of lung cancer cell proliferation depends on IGFBP-5 and PIWIL1 expression levels.

Mark E. Reeves,Yousef G. Amaar,Shin-Tai Chen,Matthew Firek,Pierlorenzo Pallante

doi:10.1371/journal.pone.0101679

Mark E. Reeves, Yousef G. Amaar + Show 3 more

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https://doi.org/10.1371/journal.pone.0101679

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Abstract

RASSF1C is a major isoform of the RASSF1 gene, and is emerging as an oncogene. This is in contradistinction to the RASSF1A isoform, which is an established tumor suppressor. We have previously shown that RASSF1C promotes lung cancer cell proliferation and have identified RASSF1C target genes with growth promoting functions. Here, we further report that RASSF1C promotes lung cancer cell migration and enhances lung cancer cell tumor sphere formation. We also show that RASSF1C over-expression reduces the inhibitory effects of the anti-cancer agent, betulinic acid (BA), on lung cancer cell proliferation. In previous work, we demonstrated that RASSF1C up-regulates piwil1 gene expression, which is a stem cell self-renewal gene that is over-expressed in several human cancers, including lung cancer. Here, we report on the effects of BA on piwil1 gene expression. Cells treated with BA show decreased piwil1 expression. Also, interaction of IGFBP-5 with RASSF1C appears to prevent RASSF1C from up-regulating PIWIL1 protein levels. These findings suggest that IGFBP-5 may be a negative modulator of RASSF1C/ PIWIL1 growth-promoting activities. In addition, we found that inhibition of the ATM-AMPK pathway up-regulates RASSF1C gene expression.

Highlights

The RASSF1 gene plays an important role in human cancer cell growth and progression
Because the anti-cancer agent, betulinic acid (BA), has been shown to down-regulate PIWIL1 gene expression [22], we studied the effects of BA and RASSF1C/ insulin-like growth factor binding protein 5 (IGFBP-5) interaction on PIWIL1 gene expression and b-catenin protein levels
SP cells did over-express RASSF1C (Figure 3B). All of this suggests that RASSF1C may enhance lung cancer stem cell proliferation, and it is possible that this happens through up-regulation of PIWIL1 gene, a stem cell self-renewal gene [12]

Summary

Introduction

The RASSF1 gene plays an important role in human cancer cell growth and progression. It encodes multiple isoforms, the major ones of which are RASSF1A and RASSF1C. RASSF1A is the most frequently inactivated tumor suppressor in human cancers mainly by means of specific promoter methylation It inhibits cell growth and migration, and promotes apoptosis. The RASSF1 gene appears to play an important dual role in cancer, functioning alternatively as a tumor suppressor and as an oncogene [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15] Consistent with this concept, recent studies show that the expression of RASSF1C is up-regulated in human lung carcinoma tissue compared to matched normal tissues, and is associated with cancer progression and poor prognosis [13]. RASSF1C over-expression (but not RASSF1A over-expression) in human cancer cells enhances accumulation of the b-catenin oncogene, a key player in the Wnt signaling pathway, leading to increased transcriptional activation and cell proliferation [16]

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