Abstract 3839: RASSF1C and tumor microenvironment

Introduction: Tumor microenvironment (TME) plays a vital role in tumor invasion and metastasis and provides a rich environment for identifying novel therapeutic targets. The TME landscape consists of extracellular matrix (ECM) and stromal cells. ECM is a major component of TME that mediates interaction between cancer cells and stromal cells to promote invasion and metastasis. We have shown in published work that RASSF1C promotes cancer stem cell development, migration, and drug resistance, in part, by promoting EMT through a mechanism that involves up-regulation of the PIWIL1-piRNA gene axis. Interestingly, one of the target genes identified by our microarray study to be upregulated by RASSF1C is P4HA2. In cancer, P4H2A is vital for collagen posttranslational modification and folding. This leads to formation of a stiff ECM and induction of cancer stem cell marker gene expression, resulting in metastatic dissemination. High expression of P4HA2 is associated with significantly lower survival of lung cancer patients. Thus, RASSF1C could promote tumor cell ECM remodeling to induce lung cancer cell stemness, invasion and metastasis by up-regulating a novel PIWIL1-P4HA2 gene axis expression.

Methods: Analysis of a microarray study using H1299 cells over-expressing RASSF1C or control vector backbone identified P4HA2 as a RASSF1C gene target. RT-PCR, immunoblots, and immunofluorescence techniques were used to confirm P4HA2 gene expression using specific primers and antibodies in cells over-expressing RASSF1C or PIWIL1 along with control cells. Kaplan-Meier analysis was performed to determine the relationship of P4HA2 expression to lung adenocarcinoma patient survival using data from The Cancer Genome Atlas (TCGA).

Results: Analysis of microarray data from H1299 cells over-expressing RASSF1C or control vector backbone shows that RASSF1C up-regulates P4HA2 gene expression 2-fold. The up-regulation of P4HA2 expression by RASSF1C was confirmed by RT-PCR, immunoblots, and immunofluorescence using P4HA2 gene specific primers and antibodies. Further, H1299 cells over-expressing PIWIL1 show increased P4HA2 gene expression on immunoblots. Kaplan-Meier analysis shows that high P4HA2 expression in lung adenocarcinoma patients negatively correlates with patient survival. Thus, our findings suggest the hypothesis that RASSF1C may promote lung cancer cell ECM remodeling to induce lung cancer cell stemness, invasion and metastasis, in part, by up-regulating a novel pathway involving a PIWIL1-P4HA2 gene axis.

Conclusions: Investigating the role of a RASSF1C-PIWIL1-P4HA2 gene axis in ECM remodeling in lung cancer cells will provide important mechanistic information that could, in turn, lead to identification of useful biomarkers for lung cancer prognosis and targets for therapy.

Citation Format: Yousef G. Amaar, Mark E. Reeves. RASSF1C and tumor microenvironment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3839.

The impact of the RASSF1C and PIWIL1 on DNA methylation: the identification of GMIP as a tumor suppressor

INTRODUCTION

Recently we have identified a novel RASSF1C-PIWIL1-piRNA pathway that promotes lung cancer cell progression and migration. PIWI-like proteins interact with piRNAs to form complexes that regulate gene expression at the transcriptional and translational levels. We have illustrated in previous work that RASSF1C modulates the expression of the PIWIL1-piRNA gene axis, suggesting the hypothesis that the RASSF1C-PIWI-piRNA pathway could potentially contribute to lung cancer stem cell development and progression, in part, through modulation of gene methylation of both oncogenic and tumor suppressor genes. Therefore, we tested this hypothesis using a non-small cell lung cancer (NSCLC) cell model to identify Candidate Differentially Methylated Regions (DMRs) modulated by the RASSF1C-PIWIL1-piRNA pathway.

MATERIALS AND METHODS

We studied the impact of over-expressing RASSF1C and knocking down RASSF1C and PIWIL1 expression on global gene DNA methylation in the NSCLC cell line H1299 using the Reduced Representation Bisulfite Sequencing (RRBS) method.

RESULTS

DMRs were identified by comparing DNA methylation profiles of experimental and control cells. Over-expression of RASSF1C and knocking down RASSF1C and PIWIL1 modulated DNA methylation of genomic regions; and statistically significant candidate genes residing DMR regions in lung cancer cells were identified, including oncogenes and tumor suppressors. One of the hypermethylated genes, Gem Interacting Protein (GMIP), displays tumor suppressor properties. GMIP expression attenuates lung cancer cell migration, and its over-expression is associated with longer survival of lung cancer patients.

CONCLUSIONS

The RASSF1C-PIWI-piRNA pathway modulates key oncogenes and tumor suppressor genes. GMIP is hypermethylated by this pathway and has tumor suppressor properties.

Abstract 5304: Gem-interacting protein (Gmip) is potentially a new lung tumor suppressor

Introduction: We have identified a novel RASSF1C-PIWIL1-piRNA pathway that appears to promote lung cell proliferation and migration. PIWI-like proteins interact with PIWI interacting RNAs (piRNAs) to form complexes that regulate gene expression at the transcriptional and post-transcriptional levels leading to stimulation of stem cell renewal and proliferation. We previously have shown that RASSF1C regulates the expression of the PIWIL1-piRNA gene axis, suggesting the hypothesis that the RASSF1C-PIWI-piRNA pathway may promote lung cancer stem cell development and progression, in part, by epigenetically modulating the expression of growth promoting and growth inhibiting genes. To validate this hypothesis, we used a non-small cell lung cancer cell model to identify candidate genes targeted by the RASSF1C-PIWIL1-piRNA pathway through a gene methylation mechanism.

Methods: We have previously conducted a study to assess the impact of over-expressing RASSF1C and knocking down RASSF1C and P1WIL1 expression on global gene DNA methylation in the NSCLC cell line H1299 using the Reduced Representation Bisulfite Sequencing method. Candidate Differentially Methylated Regions (DMR) were identified by comparing DNA methylation profiles of experimental and control cells. Statistically significant candidate genes residing in hypo- and hyper-methylated regions in lung cancer cells were identified.

Results: We found that over-expression of RASSF1C and knocking down RASSF1C and PIWIL1 modulated DNA methylation of genomic regions. Among the candidate target genes identified is Gmip, a RhoA-specific GTPase-activating protein. We found over-expression of RASSF1C increases and knock-down of RASSF1C or PIWIL1 decreases intragenic methylation of Gmip. Consistent with this, RT-PCR analysis shows that Gmip mRNA levels are reduced in lung cancer cells over-expressing RASSF1C while Gmip mRNA levels are increased in cells with RASSF1C or PIWIL1 knocked down. Further, Kaplan-Meier analysis of survival of lung adenocarcinoma patients in The Cancer Genome Atlas shows that high expression of Gmip is associated with significantly higher patient survival, suggesting that Gmip may function as a tumor suppressor.

Conclusion: The RASSF1C-PIWI-piRNA pathway may drive epigenome regulation and genesis of lung cancer stem cells through modulation of novel genes such as Gmip. Interestingly, Gmip is among 3781 mRNAs that are predicted to be targeted by the PIWIL1-piRNA complex in mouse male germ cells. Our findings are the first to suggest that Gmip is a human lung tumor suppressor. Since virtually nothing is known about Gmip function in human cancer, its function as a tumor suppressor in lung cancer needs to be studied and characterized.

Citation Format: Yousef G. Amaar, Mark E. Reeves. Gem-interacting protein (Gmip) is potentially a new lung tumor suppressor [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 5304.

RASSF1C regulates miR-33a and EMT marker gene expression in lung cancer cells

RASSF1C functions as an oncogene in lung cancer cells by stimulating proliferation and migration, and reducing apoptosis. Further, RASSF1C up-regulates important protein-coding and non-coding genes involved in lung cancer cell growth, including the stem cell self-renewal gene, piwil1, and small noncoding PIWI-interacting RNAs (piRNAs). In this article, we report the identification of microRNAs (miRNAs) that are modulated in lung cancer cells over-expressing RASSF1C. A lung cancer-specific miRNA PCR array screen was performed to identify RASSF1C target miRNA-coding genes using RNA isolated from the lung cancer cell line H1299 stably over-expressing RASSF1C and corresponding control. Several modulated miRNA genes were identified that are important in cancer cell proliferation and survival. Among the miRNAs down-regulated by RASSF1C is miRNA-33a-5p (miRNA-33a), which functions as a tumor suppressor in lung cancer cells. We validated that over-expression of RASSF1C down-regulates miR-33a expression and RASSF1C knockdown up-regulates miR-33a expression. We found that RASSF1C over-expression also increases β-catenin, vimentin, and snail protein levels in cells over-expressing miR-33a. In addition, we found that RASSF1C up-regulates the expression of ABCA1 mRNA which is a known target of miR-33a. Our findings suggest that RASSF1C may promote lung epithelial mesenchymal transition (EMT), resulting in the development of a lung cancer stem cell phenotype, progression, and metastasis, in part, through modulation of miR-33a expression. Our findings reveal a new mechanistic insight into how RASSF1C functions as an oncogene.

Abstract 365: The impact of the RASSF1C-PIWIL1-piRNA pathway on DNA methylation

Introduction: Epigenomic regulation is becoming critically important in human cancers as epigenetically regulated genes can be used as biomarkers for diagnosis, prognosis, molecular classification of tumors, and predicting response to therapies. Hence, identification of epigenetic biomarkers for specific cancers is highly desirable for development of precision medicine tools. Recently we have identified a novel RASSF1C-PIWIL1-piRNA pathway that appears to promote lung cell proliferation and migration. PIWI-like proteins interact with piRNAs to form complexes that regulate gene expression at the transcriptional (epigenetic control) and translational (mRNA silencing) levels, leading to stimulation of cell stem renewal and proliferation. We have shown that RASSF1C modulates the PIWIL1-piRNA gene axis, suggesting the hypothesis that the RASSF1C-PIWI-piRNA pathway could potentially contribute to lung cancer stem cell development and progression, in part, through modulation of gene methylation of both oncogenic and tumor suppressor genes. Thus, we wanted to validate this hypothesis using a non-small cell lung cancer (NSCLC) cell model to determine if we can identify candidate genes targeted by the RASSF1C-PIWIL1-piRNA pathway through a gene methylation mechanism.

Methods: We conducted a pilot study on the impact of over-expressing RASSF1C and knocking down RASSF1C and P1WIL1 expression on global gene DNA methylation in the NSCLC cell line H1299. DNA from cells over-expressing RASSF1C, RASSF1C-knockdown, PIWIL1-knockdwn, and control cells was used for the methylation study using the Reduced Representation Bisulfite Sequencing (RRBS) method.

Results: Candidate Differentially Methylated Regions (DMR) were identified by comparing DNA methylation profiles of experimental and control cells. We found that over-expression of RASSF1C and knocking down RASSF1C and PIWIL1 modulated DNA methylation of genomic regions; and statistically significant candidate genes residing in hypo- and hyper-methylated regions in lung cancer cells were identified, including the Dual-specificity phosphatase 4 gene (DUSP4) that functions as a tumor suppressor.

Conclusion: The RASSF1C-PIWI-piRNA pathway may play a critical role in epigenome regulation and genesis of lung cancer stem cells through modulation of key genes such as DUSP4. We found that RASSSF1C over-expression increases, while knock-down of RASSF1C or PIWIL1 decreases methylation/expression of the DUSP4 gene perhaps providing a potential mechanism through which the RASSF1C-PIWIL1-piRNA pathway could promote lung cancer stem cell development and progression. DUSP4 is an interesting target gene because knockdown of DUSP4 has recently been shown to enhance cancer stem cell formation.

Citation Format: Yousef G. Amaar, Mark E. Reeves. The impact of the RASSF1C-PIWIL1-piRNA pathway on DNA methylation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 365.

Identification and characterization of RASSF1C piRNA target genes in lung cancer cells

RASSF1C up-regulates important genes involved in lung cancer cell growth, including a stem cell self-renewal gene, piwil1. In this article, we report the identification of small noncoding PIWI-interacting RNAs (piRNAs) in lung cancer cells over-expressing RASSF1C. A piRNA microarray screen was performed using RNA isolated from the lung cancer cell line H1299 stably over-expressing RASSF1C and corresponding control. The piRNA microarray screen identified several piRNAs that are regulated by RASSF1C and we have validated the expression of two up-regulated piRNAs (piR-34871 and piR-52200) and two down-regulated piRNAs (piR-35127 and piR-46545) in lung cancer cells with silenced and over-expressed RASSF1C using RT-PCR. We also assessed the expression of these four piRNAs in lung tumor and matched normal tissues (n = 12). We found that piR-34871 and piR-52200 were up-regulated in 58% and 50%, respectively; while piR-35127 and piR-46545 were down-regulated in 50% in lung tumor tissues tested. The expression of piR-35127 was inversely correlated with RASSF1C expression in 10/12 tumor tissues. Over-expression of piR-35127 and piR-46545 and knock-down of piR-34871 and piR-52200 significantly reduced normal lung and breast epithelial cell proliferation and cell colony formation as well as proliferation of lung cancer cell lines (A549 and H1299) and breast cancer cell lines (Hs578T and MDA-MB-231). This suggests that these novel piRNAs may potentially be involved in regulating lung cell transformation and tumorigenesis. RASSF1C may potentially modulate the expression of its piRNA target genes through attenuation of the AMPK pathway, as over-expression of RASSF1C resulted in reduction of p-AMPK, p21, and p27 protein levels.

Abstract 2146: RASSF1C modulation of Piwi-interacting RNAs (piRNAs) in lung cancer

Introduction: RASSF1C is emerging as an important oncoprotein in lung cancer cell growth. We have shown that RASSF1C promotes lung cancer cell proliferation and migration; and RASSF1C up-regulates important genes in lung cancer cell growth that include a stem cell self-renewal gene, piwi1 (hiwi). PIWI-like proteins are a subfamily of Argonaute proteins that interact with small PIWI-interacting RNA molecules (known as piRNAs that are 24-32 nucleotides long) to form complexes that regulate transcriptional and translational repression. This leads to inhibition of apoptosis, stimulation of cell division and proliferation, and down-regulation of cyclin inhibitors and tumor suppressors. Therefore, modulation of Piwil1-piRNA gene expression by RASSF1C suggests a potential role for RASSF1C in lung cancer stem cell development and progression. To further investigate our hypothesis, we carried out a global piRNA microarray screen to identify piRNAs that are modulated by RASSF1C in lung cancer cells.

Method: A piRNA microarray screen was performed using the lung cancer cell line H1299 stably over-expressing RASSF1C (and controls). Total RNA was extracted from experimental and control cells and was submitted to Arraystar (Rockville, MD) for the piRNA microarray screen and data analysis.

Results: The piRNA microarray screen identified several piRNAs that are regulated by RASSF1C and we have confirmed the expression of some of them in cell lines. The function of the piRNAs identified is yet to be determined. We have initiated studies to determine the function of some of the most up-regulated and down-regulated piRNA genes in lung cancer cells. We are also profiling the expression of these piRNAs in normal and lung tumor tissues.

Conclusion: Several piRNAs are target genes of RASSF1C. Characterization of the function of these piRNAs may enhance our understanding of the role of RASSF1C in promoting lung cancer stem cell growth and progression. Linking a Rassf1c-Piwil1/piRNAs axis to lung cancer stem cell development and progression could possibly lead to discovery of new diagnostic and therapeutic targets for lung cancer.

Citation Format: Yousef G. Amaar, Matthew Firek, Mark E. Reeves, Mark E. Reeves. RASSF1C modulation of Piwi-interacting RNAs (piRNAs) in lung cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2146. doi:10.1158/1538-7445.AM2015-2146

Abstract 2454: Ampk and hdac pathways and regulation rassf1c gene expression

Introduction: We have previously shown that RASSF1C promotes cell proliferation, migration and attenuates apoptosis in cancer cells. We have also shown that RASSF1C is significantly up-regulated in breast and lung cancer tissues compared to normal tissues. Together these demonstrate that RASSF1C, is not a tumor suppressor like RASSF1A, but instead appears to function as an oncoprotein.

Currently nothing is known about the upstream signaling cascades involved in regulating RASSF1C gene expression and thus we performed transcriptome PCR array study to identify chemicals inhibitors that modulate(s) RASSF1C expression.

Method: A transcriptome PCR array was obtained from Qiagen. It consisted of cDNA from breast cancer cell line MCF7 cells treated with 90 different chemical inhibitors that regulate various signaling pathways. The array was screened with RASSF1C gene specific primers. Data analysis was performed by importing the Ct values obtained into data analysis software.

Results: The PCR array screen identified several chemical reagents that appear to up-regulate and several that seem to down-regulate RASSF1C expression by ≥ 1.5 fold. The two most notable reagents are Dorsopmorhin (AMPK inhibitor) which up-regulates RASSF1C expression by 2.8 fold and Trichostatin A (HDAC inhibitor) which down regulates RASSF1C expression by 2 fold. We are in process of confirming the effect of these inhibitors in a panel of breast and lung cancer cells.

Conclusion: The findings are novel and suggest that inhibition of AMPK pathway induces RASSF1C expression while inhibition of HDAC pathway suppresses RASSF1C gene expression. We should note that Trichostatin A has been shown to activate AMPK, inhibits HDAC, arrests cell growth, and induces apoptosis in human cancers. Our findings provide a potential mechanism for regulating RASSF1C gene expression through the modulation of AMPK and HDAC pathways.

Citation Format: Yousef G. Amaar, Mark E. Reeves, Matthew Firek. Ampk and hdac pathways and regulation rassf1c gene expression. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2454. doi:10.1158/1538-7445.AM2014-2454

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

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.

Abstract 4288: RASSF1C, unlike RASSF1A, reduces TNF-α induced phosphorylation of MST1/2

Introduction: Recently, RASSF1A has been shown to mediate the apoptotic effects of TNF-α by interacting with the mammalian sterile 20-like kinase 1 and 2 (MST1/2) through the Salvador/Rassf/Hippo (SARAH) domain leading to MST1/2 phosphorylation activation of apoptosis through the Hippo pathway. In contrast, we have previously shown that RASSF1C promotes cell proliferation and attenuates apoptosis in cancer cells. Since both RASSF1A and RASSF1C contain the SARAH domain located in their identical C-termini, RASSF1C should be capable of interacting with SARAH domain-containing proteins, and could potentially attenuate MST1/2-mediated apoptosis through the Hippo pathway. Thus, in this study we have investigated the impact of RASSF1C on MST1/2 activation/phosphorylation in presence of TNF-α, including whether RASSF1C modulates MST1/2 pro-apoptotic effects through the Hippo pathway differently from RASSF1A.

Method: Breast and lung cancer cells over-expressing RASSF1A and RASSF1C were used in this study. Cells were cultured in the proper media and treated with TNF-α for 12-18 hr. Cells were collected and used for Western blot analysis utilizing antibodies that detect MST and p-MST antibodies.

Results: Our preliminary data suggest that RASSF1C over-expression decreases the phosphorylation levels of MST1/2 in TNF-α-treated breast and lung cancer cells compared to those cells over-expressing RASSF1A

Conclusion: Our findings suggest that over-expression of RASSF1C in breast and lung cancer cells may attenuate the MST1/2 apoptotic effects by sequestering of MST1/2 proteins and inhibiting their activation by phosphorylation. The findings also further support our hypothesis that RASSF1C attenuates apoptosis; and RASSF1C, unlike RASSF1A, may inhibit MST1/2 activation and hence may negatively modulate the Hippo pathway.

Citation Format: Yousef G. Amaar, Matthew Firek, Mark E. Reeves. RASSF1C, unlike RASSF1A, reduces TNF-α induced phosphorylation of MST1/2. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4288. doi:10.1158/1538-7445.AM2013-4288

Ras-Association Domain Family 1C Protein Enhances Breast Tumor Growth in Vivo

The Ras association domain family 1 (RASSF1) gene is a Ras effector that plays an important role in carcinogenesis. We have previously shown that silencing of RASSF1C decreases and over-expression of RASSF1C increases cell proliferation, migration, and attenuates apoptosis of breast cancer cells in vitro. To further confirm our working hypothesis that RASSF1C may play a role as a growth promoter, we have tested the growth of human breast cancer cells stably over-expressing RASSF1A or RASSF1C in nude mice. Our studies show that breast cancer cells over-expressing HA-RASSF1A developed significantly smaller tumors and cells over-expressing HA-RASSF1C developed significantly larger tumors compared to control cells expressing the vector back bone. We have confirmed the expression of HA-RASSF1A and HA-RASSF1C in tumor tissue using RT-PCR, western blotting and immunohistochemical analyses using HA-antibody. Together, our previous in vitro and current in vivo findings further support our hypothesis that RASSF1C, unlike RASSF1A, is not a tumor suppressor and rather it appears to function as tumor growth promoter in breast cancer cells.

RASSF1C modulates the expression of a stem cell renewal gene, PIWIL1

Background

RASSF1A and RASSF1C are two major isoforms encoded by the Ras association domain family 1 (RASSF1) gene through alternative promoter selection and mRNA splicing. RASSF1A is a well established tumor suppressor gene. Unlike RASSF1A, RASSF1C appears to have growth promoting actions in lung cancer. In this article, we report on the identification of novel RASSF1C target genes in non small cell lung cancer (NSCLC).

Methods

Over-expression and siRNA techniques were used to alter RASSF1C expression in human lung cancer cells, and Affymetrix-microarray study was conducted using NCI-H1299 cells over-expressing RASSF1C to identify RASSF1C target genes.

Results

The microarray study intriguingly shows that RASSF1C modulates the expression of a number of genes that are involved in cancer development, cell growth and proliferation, cell death, and cell cycle. We have validated the expression of some target genes using qRT-PCR. We demonstrate that RASSF1C over-expression increases, and silencing of RASSF1C decreases, the expression of PIWIL1 gene in NSCLC cells using qRT-PCR, immunostaining, and Western blot analysis. We also show that RASSF1C over-expression induces phosphorylation of ERK1/2 in lung cancer cells, and inhibition of the MEK-ERK1/2 pathway suppresses the expression of PIWIL1 gene expression, suggesting that RASSF1C may exert its activities on some target genes such as PIWIL1 through the activation of the MEK-ERK1/2 pathway. Also, PIWIL1 expression is elevated in lung cancer cell lines compared to normal lung epithelial cells.

Conclusions

Taken together, our findings provide significant data to propose a model for investigating the role of RASSF1C/PIWIL1 proteins in initiation and progression of lung cancer.

Abstract 1139: Ras association domain family protein 1, isoform C (RASSF1C) promotes breast tumor growth in vivo

Breast cancer will kill more than 40,000 women in the United States this year, second in cancer deaths only to carcinoma of the lung. Therefore, a better understanding of the molecules and pathways that lead to breast cancer development is important because it could lead to specific therapies that interrupt these pathways. Recently, the Ras association domain family 1 (RASSF1) gene was identified as a Ras effector that plays an important role in carcinogenesis. The RASSF1 gene encodes two major isoforms, RASSF1A and RASSF1C, derived by alternative promoter selection and alternative mRNA splicing. While RASSF1A is extensively studied and is an established tumor suppressor, very little is known about RASSF1C function

Our laboratory is interested in determining the role of RASSF1C in human cancer cell growth. We have previously shown that of RASSF1C promotes cell proliferation and migration and attenuates apoptosis of breast cancer cells in vitro. To confirm our hypothesis that RASSF1C may be a growth promoter, we have tested the growth of human breast cancer cells over-expressing RASSF1C in nude mice. Our preliminary studies show that breast cancer cells over-expressing RASSF1C developed significantly larger tumors compared to control cells. We have confirmed the expression of RASSF1C in tumor tissue using both RT-PCR and immune-staining analyses. Together, our previous in vitro and current in vivo findings further support our hypothesis that RASSF1C, unlike RASSF1A, is not a tumor suppressor and rather it appears to play a role in stimulating proliferation and survival of breast cancer cells.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1139. doi:10.1158/1538-7445.AM2011-1139

Ras-association domain family 1C protein promotes breast cancer cell migration and attenuates apoptosis

Background

The Ras association domain family 1 (RASSF1) gene is a Ras effector encoding two major mRNA forms, RASSF1A and RASSF1C, derived by alternative promoter selection and alternative mRNA splicing. RASSF1A is a tumor suppressor gene. However, very little is known about the function of RASSF1C both in normal and transformed cells.

Methods

Gene silencing and over-expression techniques were used to modulate RASSF1C expression in human breast cancer cells. Affymetrix-microarray analysis was performed using T47D cells over-expressing RASSF1C to identify RASSF1C target genes. RT-PCR and western blot techniques were used to validate target gene expression. Cell invasion and apoptosis assays were also performed.

Results

In this article, we report the effects of altering RASSF1C expression in human breast cancer cells. We found that silencing RASSF1C mRNA in breast cancer cell lines (MDA-MB231 and T47D) caused a small but significant decrease in cell proliferation. Conversely, inducible over-expression of RASSF1C in breast cancer cells (MDA-MB231 and T47D) resulted in a small increase in cell proliferation. We also report on the identification of novel RASSF1C target genes. RASSF1C down-regulates several pro-apoptotic and tumor suppressor genes and up-regulates several growth promoting genes in breast cancer cells. We further show that down-regulation of caspase 3 via overexpression of RASSF1C reduces breast cancer cells' sensitivity to the apoptosis inducing agent, etoposide. Furthermore, we found that RASSF1C over-expression enhances T47D cell invasion/migration in vitro.

Conclusion

Together, our findings suggest that RASSF1C, unlike RASSF1A, is not a tumor suppressor, but instead may play a role in stimulating metastasis and survival in breast cancer cells.

Ras association domain family 1C protein stimulates human lung cancer cell proliferation

Recently, the Ras association domain family 1 gene (RASSF1) has been identified as a Ras effector encoding two major mRNA forms, RASSF1A and RASSF1C, derived by alternative promoter selection and alternative mRNA splicing. RASSF1A is a tumor suppressor gene. However, the function of RASSF1C, both in normal and cancer cells, is still unknown. To learn more about the function of RASSF1C in human cancer cells, we tested the effect of silencing RASSF1C mRNA with small interfering RNA on lung cancer cells (NCI H1299) that express RASSF1C but not RASSF1A. Small interfering RNA specific for RASSF1C reduced RASSF1C mRNA levels compared with controls. This reduction in RASSF1C expression caused a significant decrease in lung cancer cell proliferation. Furthermore, overexpression of RASSF1C increased cell proliferation in lung cancer cells. Finally, we found that RASSF1C, unlike RASSF1A, does not upregulate N-cadherin 2 and transglutaminase 2 protein expression in NCI H1299 lung cancer cells. This suggests that RASSF1C and RASSF1A have different effector targets. Together, our findings suggest that RASSF1C, unlike RASSF1A, is not a tumor suppressor but rather stimulates lung cancer cell proliferation.

Identification and characterization of novel IGFBP5 interacting protein: evidence IGFBP5-IP is a potential regulator of osteoblast cell proliferation

Insulin-like growth factor binding protein-5 (IGFBP5) is a multifunctional protein, which acts not only as a traditional binding protein, but also functions as a growth factor independent of IGFs to stimulate bone formation. It has been predicted that the intrinsic growth factor action of IGFBP5 involves binding of IGFBP5 to a putative receptor to induce downstream signaling pathways and/or nuclear translocation of IGFBP5 to influence transcription of genes involved in osteoblast cell proliferation/differentiation. Our study indentified proteins that bound to IGFBP5 using IGFBP5 as bait in a yeast two-hybrid screen of the U2 human osteosarcoma cell cDNA library. One of the clones that interacted strongly with the bait under high-stringency conditions corresponded to a novel IGFBP5 interacting protein (IGFBP5-IP) encoded by a gene that resides in mouse chromosome 10. The interaction between IGFBP5-IP and IGFBP5 is confirmed by in vitro coimmunoprecipitation studies that used pFlag and IGFBP5 polyclonal antibody, and cell lysates overexpressing both IGFBP5-IP and IGFBP5. Northern blot and RT-PCR analysis showed that the IGFBP-IP is expressed in both untransformed normal human osteoblasts and in osteosarcoma cell lines, which are known to produce IGFBP5. To determine the roles of IGFBP5-IP, we evaluated the effect of blocking the expression of IGFBP5-IP on osteoblast proliferation. We found that using a IGFBP5-IP-specific small interfering-hairpin plasmid resulted in a decrease in both basal and IGFBP5-induced osteoblast cell proliferation. On the basis of these findings, we predict that IGFBP5-IP may act as intracellular mediator of growth promoting actions of IGFBP5 and perhaps other osteoregulatory agents in bone cells.

Ras-association domain family 1 protein, RASSF1C, is an IGFBP-5 binding partner and a potential regulator of osteoblast cell proliferation

The goal of this study was to identify downstream signaling molecules involved in mediating the IGF-independent effects of IGFBP-5 in osteoblasts. We identified RASSF1C, a member of the RASSF1 gene products, as a IGFBP-5 binding partner and as a potential mediator of IGFBP-5 effects on ERK phosphorylation and cell proliferation.

INTRODUCTION

It has been predicted that the intrinsic growth factor action of insulin-like growth factor binding protein (IGFBP)-5 involves either the binding of IGFBP-5 to a putative receptor to induce downstream signaling pathways and/or intracellular translocation of IGFBP-5 to bind to potential signaling molecules involved in osteoblast cell regulation. This study reports the characterization of isoform C of the Ras association family 1 (RASSF1C) gene as an interacting partner of IGFBP-5.

MATERIALS AND METHODS

IGFBP-5 was used as bait in a yeast two-hybrid screen of a human osteosarcoma cDNA library. Expression levels of RASSF1C were measured by RT-PCR and/or Northern blot. IGFBP-5 effects on ERK phosphorylation were evaluated by immunoblot analysis. The effect of RASSF1C siRNA on cell proliferation was measured by the AlamarBlue assay.

RESULTS

One of the clones that interacted strongly with the bait under high stringency conditions corresponded to RASSF1C. The interaction between RASSF1C and IGFBP-5 was confirmed by in vitro co-immunoprecipitation studies. Northern blot and RT-PCR analysis showed that RASSF1C was expressed in a variety of osteoblast cell types that produce IGFBP-5. Addition of synthetic RASSF1C-specific small interfering (si) RNA duplex or use of a RASSF1C-specific si-hairpin plasmid caused a decrease in cell number and abolished IGFBP-5-induced extracellular signal-regulated kinase (ERK)-1/2 phosphorylation but had no effect on IGFBP-5-induced increases in alkaline phosphatase (ALP) activity.

CONCLUSIONS

We have shown a novel interaction between IGFBP-5 and RASSF1C. Our findings that silencing of RASSF1C results in the reduction of osteoblast cell proliferation and that IGFBP-5 treatment increases phosphorylation of ERK-1/2 raise the possibility that RASSF1C, a Ras effector, could, in part, contribute to mediating the effects of IGFBP-5 on ERK phosphorylation and, consequently, cell proliferation.

ADAM-9 is an insulin-like growth factor binding protein-5 protease produced and secreted by human osteoblasts

IGF binding protein-5 (BP-5) is an important bone formation regulator. Therefore, elucidation of the identity of IGF binding protein-5 (BP-5) protease produced by osteoblasts is important for our understanding of the molecular pathways that control the action of BP-5. In this regard, BP-5 protease purified by various chromatographic steps from a conditioned medium of U2 human osteosarcoma cells migrated as a single major band, which comigrated with the protease activity in native PAGE and yielded multiple bands in SDS-PAGE under reducing conditions. N-Terminal sequencing of these bands revealed that three of the bands yielded amino acid sequences that were identical to that of alpha2 macroglobulin (alpha2M). Although alpha2M was produced by human osteoblasts (OBs), it was not found to be a BP-5 protease. Because alpha2M had been shown to complex with ADAM proteases and because ADAM-12 was found to cleave BP-3 and BP-5, we evaluated if one of the members of ADAM family was the BP-5 protease. On the basis of the findings that (1) purified preparations of BP-5 protease from U2 cell CM contained ADAM-9, (2) ADAM-9 is produced and secreted in high abundance by various human OB cell types, (3) purified ADAM-9 cleaved BP-5 effectively while it did not cleave other IGFBPs or did so with less potency, and (4) purified ADAM-9 bound to alpha2M, we conclude that ADAM-9 is a BP-5 protease produced by human OBs.

Insulin-like growth factor-binding protein 5 (IGFBP-5) interacts with a four and a half LIM protein 2 (FHL2)

Recent studies using insulin-like growth factor I (IGF-I) knockout mice demonstrate that IGF-binding protein (IGFBP)-5, an important bone formation regulator, itself is a growth factor with cellular effects not dependent on IGFs. Because IGFBP-5 contains a nuclear localization sequence that mediates transport of IGFBP-5 into the nucleus, we propose that IGFBP-5 interacts with nuclear proteins to affect transcription of genes involved in bone formation. We therefore undertook studies to identify proteins that bind to IGFBP-5 using IGFBP-5 as bait in a yeast two-hybrid screen of a U2 human osteosarcoma cDNA library. Five related clones that interacted strongly with the bait corresponded to the FHL2 gene, which contains four and a half LIM domains. Co-immunoprecipitation studies with lysates from U2 cells overexpressing FHL2 and IGFBP-5 confirmed that interaction between IGFBP-5 and FHL2 occurs in whole cells. In vitro interaction studies revealed that purified FHL2 interacted with IGFBP-5 but not with IGFBP-3, -4, or -6. Northern blot analysis showed that FHL2 was strongly expressed in human osteoblasts. Nuclear localization of both FHL2 and IGFBP-5 was evident from Western immunoblot analysis and immunofluorescence. The role of FHL2 as an intracellular mediator of the effects of IGFBP-5 and other osteoregulatory agents in osteoblasts will need to be verified in future studies.

Mapping of the nitrate-assimilation gene cluster (crnA-niiA-niaD) and characterization of the nitrite reductase gene (niiA) in the opportunistic fungal pathogen Aspergillus fumigatus

This study reports the molecular characterization of the nitrate-assimilation gene cluster from the opportunistic fungal pathogen Aspergillus fumigatus. A genomic fragment was isolated which contained the entire structural gene encoding nitrite reductase (niiA), plus segments of the nitrate reductase (niaD) and the nitrate transporter (crnA) genes. Nitrate-assimilation genes in A. fumigatus are physically linked and transcribed in the same direction as in A. nidulans. The nitrate-assimilation gene cluster is on the largest chromosome (5.3 Mb). The nitrite reductase (niiA) gene encodes a protein of 1110 amino acids that contains regions corresponding to FAD, NADPH, FeS and siroheme binding sites. Eight small introns interrupt the niiA open reading frame. The niaD-niiA intergenic regulatory region contains promoter consensus sequences including TATA, CAAT, and binding sites for the areA and nirA gene products. Northern analysis indicated that the expression of niaD, niiA and crnA are induced by nitrate and repressed by ammonium at the transcriptional level.

Cloning and characterization of the C. elegans histidyl-tRNA synthetase gene

In this paper, we report the cloning and sequencing of the C. elegans histidyl-tRNA synthetase gene. The complete genomic sequence, and most of the cDNA sequence, of this gene is now determined. The gene size including flanking and coding regions is 2230 nucleotides long. Three small introns (45-50 bp long) are found to interrupt the open reading frame. The open reading frame translates to 523 amino acids. This putative protein sequence shows extensive homology with the human and yeast histidyl-tRNA the histidyl-tRNA synthetase gene is a single copy gene. Hence, it is very likely that it encodes both the cytoplasmic and the mitochondrial histidyl-tRNA synthetases. It is likely to be trans-spliced since it contains a trans-splice site in its 5' untranslated region.