The Kinase LMTK3 Promotes Invasion in Breast Cancer Through GRB2-Mediated Induction of Integrin β ₁

Abstract

Lemur tyrosine kinase 3 (LMTK3) is associated with cell proliferation and endocrine resistance in breast cancer. We found that, in cultured breast cancer cell lines, LMTK3 promotes the development of a metastatic phenotype by inducing the expression of genes encoding integrin subunits. Invasive behavior in various breast cancer cell lines positively correlated with the abundance of LMTK3. Overexpression of LMTK3 in a breast cancer cell line with low endogenous LMTK3 abundance promoted actin cytoskeleton remodeling, focal adhesion formation, and adhesion to collagen and fibronectin in culture. Using SILAC (stable isotope labeling by amino acids in cell culture) proteomic analysis, we found that LMTK3 increased the abundance of integrin subunits α5 and β1, encoded by ITGA5 and ITGB1. This effect depended on the CDC42 Rho family guanosine triphosphatase, which was in turn activated by the interaction between LMTK3 and growth factor receptor-bound protein 2 (GRB2), an adaptor protein that mediates receptor tyrosine kinase-induced activation of RAS and downstream signaling. Knockdown of GRB2 suppressed LMTK3-induced CDC42 activation, blocked ITGA5 and ITGB1 expression promoted by the transcription factor serum response factor (SRF), and reduced invasive activity. Furthermore, abundance of LMTK3 positively correlated with that of the integrin β1 subunit in breast cancer patient's tumors. Our findings suggest a role for LMTK3 in promoting integrin activity during breast cancer progression and metastasis.

LMTK3 Represses Tumor Suppressor-like Genes through Chromatin Remodeling in Breast Cancer

“…We also investigated whether the previously described proliferation advantage of LMTK3 in MCF7 cells (Xu et al, 2014) is ERa-mediated. We observed that, upon ERa removal via fulvestrant treatment, the proliferation of both MCF7 and MCF7-LMTK3 cells was significantly suppressed.…”

“…As shown previously (Xu et al, 2014), two specific LMTK3 bands are detected by western blot analysis. We now demonstrate that LMTK3 localizes both in the nucleus and in the cytoplasm of MCF7 and MDA-MB-231 cells.…”

“…However, LMTK3 is expressed in both ERa + and ERa À breast cancers, suggesting that it plays different cellular roles independent of ERa status. Our recent work has revealed that elevated cytoplasmic LMTK3 abundance in triple-negative breast cancer promotes tumor invasion and metastasis (Xu et al, 2014), which provided an example of the ERa-independent action of LMTK3. Interestingly, both nuclear and cytoplasmic expression of LMTK3 are correlated with tumor grade and patient survival (Stebbing et al, 2012).…”

PEITC inhibits human brain glioblastoma GBM 8401 cell migration and invasion through the inhibition of uPA, Rho A, and Ras with inhibition of MMP-2, -7 and -9 gene expression

“…The enhanced invasive capacity of peritumoral cells in GBM requires simultaneous Rac and RhoA activation (29). Knockdown of GRB2, mediating receptor tyrosine kinase-induced activation of RAS and downstream signaling, can reduce invasive activity of breast cancer (30). Epidermal growth factor receptor (EGFR) vIII-mediated migration and transformation of u87MG (PTEN-mutant) glioblastoma cells was found to be downregulated by the effects of signal regulatory protein α1 (SIRPα1) on the activation loop of ShP-2/FAK/GRB2/SOS-1/MAPK (31).…”

The role of LMTK3 in chromatin remodeling and transcriptional regulation

“…It is also implicated in endocrine resistance in breast cancer [20] and can promote tumor invasion and metastasis by activating the transcription of integrins [21] . Interestingly, LMTK3 is one of the few positively selected RTKs between humans and chimpanzees; considering the fact that chimpanzees have much lower susceptibility to breast cancer, this indicates the crucial role of LMTK3 in this disease [19] .…”