PtdIns(3,4,5)P3-dependent Rac Exchanger 1 (PREX1) Rac-Guanine Nucleotide Exchange Factor (GEF) Activity Promotes Breast Cancer Cell Proliferation and Tumor Growth via Activation of Extracellular Signal-regulated Kinase 1/2 (ERK1/2) Signaling

Abstract

PtdIns(3,4,5)P 3 -dependent Rac exchanger 1 (PREX1) is a Racguanine nucleotide exchange factor (GEF) overexpressed in a significant proportion of human breast cancers that integrates signals from upstream ErbB2/3 and CXCR4 membrane surface receptors. However, the PREX1 domains that facilitate its oncogenic activity and downstream signaling are not completely understood. We identify that ERK1/2 MAPK acts downstream of PREX1 and contributes to PREX1-mediated anchorage-independent cell growth. PREX1 overexpression increased but its shRNA knockdown decreased ERK1/2 phosphorylation in response to EGF/IGF-1 stimulation, resulting in induction of the cell cycle regulators cyclin D1 and p21 WAF1/CIP1. PREX1-mediated ERK1/2 phosphorylation, anchorage-independent cell growth, and cell migration were suppressed by inhibition of MEK1/2/ERK1/2 signaling. PREX1 overexpression reduced staurosporine-induced apoptosis whereas its shRNA knockdown promoted apoptosis in response to staurosporine or the anti-estrogen drug tamoxifen. Expression of wild-type but not GEF-inactive PREX1 increased anchorage-independent cell growth. In addition, mouse xenograft studies revealed that expression of wild-type but not GEF-dead PREX1 resulted in the formation of larger tumors that displayed increased phosphorylation of ERK1/2 but not AKT. The impaired anchorage-independent cell growth, apoptosis, and ERK1/2 signaling observed in stable PREX1 knockdown cells was restored by expression of wild-type but not GEF-dead-PREX1. Therefore, PREX1-Rac-GEF activity is critical for PREX1-dependent anchorage-independent cell growth and xenograft tumor growth and may represent a possible therapeutic target for breast cancers that exhibit PREX1 overexpression.The Rac proteins (Rac1, Rac2, and Rac3) are a subgroup of the Rho-GTPase family that regulate cell motility and, when deregulated, drive cancer invasion and metastasis (1-3). Rac proteins undergo rapid and spatiotemporally coordinated cycles of activation and inactivation linked to upstream receptor signaling by guanine nucleotide exchange factors (GEFs) 2 (4). The most common mechanism for Rac hyperactivation in human cancer is via dysregulation of Rac-GEF activity. PtdIns (3,4,5)P 3 -dependent Rac exchanger 1 (PREX1) is a member of the Dbl family of Rho-GEFs that promotes chemoattractantstimulated neutrophil chemotaxis and reactive O 2 species formation (5-7). PREX1 is a multidomain protein that contains an N-terminal catalytic Dbl-homologous (DH) domain, which activates Rac, adjacent to a pleckstrin homology (PH) domain, which binds to and is activated by PI3K-generated PtdIns(3,4,5)P 3 , followed by two dishevelled, EGL-10 and pleckstrin (DEP) domains, two PDZ domains, and a catalytically inactive C-terminal inositol polyphosphate 4-phosphatase (IP4P) domain, which shares 30% amino acid identity with the catalytically active IP4P domain of the inositol polyphosphate 4-phosphatases INPP4A and INPP4B (5,8,9). The IP4P domain of PREX1 contains a common catalytic CX 5 R motif shared by dual specificity p...

GLUL Promotes Cell Proliferation in Breast Cancer

“…Conventional MAPKs include p38 MAPK, extracellular signalregulated kinase 1 and 2 (ERK1/2), c-Jun N-terminal kinases/stress activated protein kinases (JNK/SAPK) and ERK5 [Arthur and Ley, 2013]. Activation of p38 MAPK [Galliher and Schiemann, 2007;Jiang et al, 2016] and ERK1/2 [Ventura et al, 2015;Liu et al, 2016] pathways are important for breast cancer cell proliferation. Sathya et al [2015] found that estrogen suppressed breast cancer proliferation through inhibiting p38 MAPK signaling pathway.…”

P-Rex1 and P-Rex2 RacGEFs and cancer

“…P-Rex1 knockdown via siRNA in multiple melanoma cell lines (CHL1, Wm793, Mel224, WM2664, Wm852) resulted in reduced invasive phenotypes [13,14,46]. P-Rex1 overexpression in breast and prostate cancer cell lines with negligible endogenous P-Rex1 expression (MDA-MB-231 and 22Rv1, respectively) increased migratory and invasive phenotypes [15,53]. However, one study reported that siRNA depletion of P-Rex1 in the DU145 prostate cancer cell line resulted in increased invasiveness, correlating with increased levels of matrix metalloproteinase 9 (MMP9) and matrix metalloproteinase 2 (MMP2), which play a role in cell invasion via extracellular matrix degradation [47].…”

“…Active P-Rex1 activates Rac, a promoter of cell cytoskeletal rearrangement, cell migration, and invasion [1,7,8]. Rac, in turns, activates PAK and the RAF/MEF/ERK signalling pathway leading to cell survival and proliferation [7,10,53]. P-Rex1 can, in some context, indirectly activate the PI3K/Akt axis [11].…”

“…The role P-Rex1 plays in cancer cell proliferation and xenograft tumour growth may vary depending on the cancer type. P-Rex1 shRNA knockdown in an ER+ breast cancer cell line (MCF-7) resulted in a marked reduction in xenograft tumour size [8,9,53]. Conversely, P-Rex1 overexpression in a triple-negative breast cancer cell line (MDA-MB-231) increased cell proliferation, anchorage-independent cell growth, and xenograft tumour growth [53].…”

“…P-Rex1 shRNA knockdown in an ER+ breast cancer cell line (MCF-7) resulted in a marked reduction in xenograft tumour size [8,9,53]. Conversely, P-Rex1 overexpression in a triple-negative breast cancer cell line (MDA-MB-231) increased cell proliferation, anchorage-independent cell growth, and xenograft tumour growth [53]. However, P-Rex1 siRNA depletion in various melanoma cell lines and overexpression in prostate cancer cell lines (PC3-LN4 and CWR22Rv1) did not affect cell proliferation and xenograft tumour growth, respectively [13][14][15].…”