RCC2 over-expression in tumor cells alters apoptosis and drug sensitivity by regulating Rac1 activation

Sheng Xiao,Yan Jin,Nan Wu,Su Li,Wenli Ma,Shaoyan Hu,Dong Ren

doi:10.1186/s12885-017-3908-y

Abstract

BackgroundSmall GTP binding protein Rac1 is a component of NADPH oxidases and is essential for superoxide-induced cell death. Rac1 is activated by guanine nucleotide exchange factors (GEFs), and this activation can be blocked by regulator of chromosome condensation 2 (RCC2), which binds the switch regions of Rac1 to prevent access from GEFs.MethodsThree cancer cell lines with up- or down-regulation of RCC2 were used to evaluate cell proliferation, apoptosis, Rac1 signaling and sensitivity to a group of nine chemotherapeutic drugs. RCC2 expression in lung cancer and ovarian cancer were studied using immunochemistry stain of tumor tissue arrays.ResultsForced RCC2 expression in tumor cells blocked spontaneous- or Staurosporine (STS)-induced apoptosis. In contrast, RCC2 knock down in these cells resulted in increased apoptosis to STS treatment. The protective activity of RCC2 on apoptosis was revoked by a constitutively activated Rac1, confirming a role of RCC2 in apoptosis by regulating Rac1. In an immunohistochemistry evaluation of tissue microarray, RCC2 was over-expressed in 88.3% of primary lung cancer and 65.2% of ovarian cancer as compared to non-neoplastic lung and ovarian tissues, respectively. Because chemotherapeutic drugs can kill tumor cells by activating Rac1/JNK pathway, we suspect that tumors with RCC2 overexpression would be more resistant to these drugs. Tumor cells with forced RCC2 expression indeed had significant difference in drug sensitivity compared to parental cells using a panel of common chemotherapeutic drugs.ConclusionsRCC2 regulates apoptosis by blocking Rac1 signaling. RCC2 expression in tumor can be a useful marker for predicting chemotherapeutic response.

Highlights

Small GTP binding protein Rac1 is a component of NADPH oxidases and is essential for superoxide-induced cell death
regulator of chromosome condensation 2 (RCC2)-YFP expression attenuated apoptosis RCC2-YFP was transiently expressed in three tumor cell lines including HeLa, lung cancer CRL5800 and breast cancer MDA-MB-231
Virtually no apoptotic cells were detected in these cells expressing RCC2-YFP (Fig. 1d & e), suggesting that RCC2-YFP expression blocked the spontaneous apoptosis of HeLa cells

Summary

Introduction

Small GTP binding protein Rac is a component of NADPH oxidases and is essential for superoxide-induced cell death. Rac is activated by guanine nucleotide exchange factors (GEFs), and this activation can be blocked by regulator of chromosome condensation 2 (RCC2), which binds the switch regions of Rac to prevent access from GEFs. RCC2 was first discovered as a telophase disk-binding protein (TD-60) [1], suggesting its role in mitosis. RCC2 shares significant similarities in primary sequence with RCC1, a known guanine nucleotide exchange factor (GEF) for Ran (ras-related nuclear protein). RCC2 bound the Rac switch regions to block Rac GEF access, leading to the attenuation of Rac activation [3]. Cells with deficient RCC2 had increased Rac activity, which was. Rac knock down results in marked decrease in both superoxide generation and superoxide -induced cell death [9]

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