Abstract 2655: Inhibitor of Differentiation/DNA binding (ID) proteins modulate the stem-like features of NSCLC cells by regulating the expression of Oct4, Sox2 and Nanog.
Authors: Bora Singhal Namrata , Perumal Deepak , Chellappan Srikumar 
Published: August 2014

Non-small cell lung cancer (NSCLC) accounts for 85% of total lung cancer cases and demonstrates a strong association with tobacco use. The overall survival rate for NSCLC patients diagnosed in the late stages of cancer is very low, demonstrating the need for novel therapeutic strategies to combat this disease. While the genetic changes contributing to lung cancer in smokers and non-smokers are fairly well characterized, the downstream signaling events involved in tumorigenesis are not fully understood. Our laboratory had identified the transcriptional regulator, ID1 (inhibitor of differentiation/DNA binding 1), as a common mediator of oncogenesis in NSCLC, irrespective of the smoking history. NSCLC tumors are heterogeneous and are either refractory to the available treatments or develop resistance to therapy. Cancer stem cells (CSC) hypothesis has emerged as an explanation for tumor initiation, drug resistance and metastasis. CSCs have been shown to have tumor initiating properties.Given that the ID gene family (ID1- ID4) is known to be expressed in the embryonic progenitor cells and have been have been suggested to promote self renewal capacity of embryonic stem cells, and since ID proteins are known to promote the genesis of NSCLC, we examined whether these proteins contribute to the stemness of NSCLC CSCs. Side-population (SP) cells with CSC properties were isolated from four different NSCLC lines using flow cytometric sorting based on Hoechst 33342 exclusion. The mRNA and protein expression of the ID1-4 genes was assessed in the sorted SP cells from these cell lines and compared to the main population (MP) cells. Among the four ID proteins, ID3 expression was found to be comparatively higher in the SP cells compared to MP cells from all the cell lines; there was a difference in the levels of other family members as well. Depletion of ID3 expression by siRNAs led to a decrease in SP frequency; further, this led to a reduced expression of embryonic stem cell transcription factors Sox2, Oct4 and Nanog expression. Similar results were obtained when ID1 was depleted as well. Interestingly, depletion of ID1 or ID3 significantly impaired the ability of SP cells to self-renew, as measured by sphere formation assays. Further analysis suggests that the transcriptional co-repressor ZBP89 might be involved in the ID-mediated repression of the ES cell transcription factors. Our findings suggest that Id proteins might play a role in the maintenance of stem like properties in NSCLC CSCs and this is facilitated by the regulation of ES cell transcription factors in a ZBP89-dependent manner. Our ongoing studies are aimed at elucidating the potential correlation of gene expression levels of ID family members with the survival of NSCLC patients, using microarray datasets.

Citation Format: Namrata Bora Singhal, Deepak Perumal, Srikumar Chellappan. Inhibitor of Differentiation/DNA binding (ID) proteins modulate the stem-like features of NSCLC cells by regulating the expression of Oct4, Sox2 and Nanog. [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 2655. doi:10.1158/1538-7445.AM2013-2655