Neoplastic Transformation Induced by the gep Oncogenes Involves the Scaffold Protein JNK-Interacting Leucine Zipper Protein

Abstract

The activated mutants of the α-subunits of G proteins G(12) and G(13) have been designated as the gep oncogenes owing to their ability to stimulate diverse oncogenic signaling pathways that lead to neoplastic transformation of fibroblast cell lines and tumorigenesis in nude mice models. Studies from our laboratory as well as others have shown that the growth-promoting activities of Gα(12) and Gα(13) involve potent activation of c-Jun N-terminal kinases (JNKs). Our previous studies have indicated that the JNK-interacting leucine zipper protein (JLP), a scaffold protein involved in the structural and functional organization of the JNK/p38 mitogen-activated protein kinase module, tethers Gα(12) and Gα(13) to the JNK signaling module. In the present study, in addition to demonstrating the physical association between JLP and Gα(12), we show that this interaction is enhanced by the receptor- or mutation-mediated activation of Gα(12). We also establish that JLP interacts with Gα(12) through the C-terminal domain that has been previously identified to be involved in binding to Gα(13). Furthermore, using this C-terminal domain as a competitively inhibitor of JLP that can disrupt Gα(12)-JLP interaction, we demonstrate that JLP is required for the stimulation of JNK by Gα(12). Our results also indicate that such JLP interaction is required for Gα(12) as well as Gα(13)-mediated neoplastic transformation of JLP. These studies demonstrate for the first time a functional role for JLP in the gep oncogene-regulated neoplastic signaling pathway.

The gep Proto-Oncogene Gα13 Mediates Lysophosphatidic Acid-Mediated Migration of Pancreatic Cancer Cells

“…Non-migrating cells on the proximal side of the inserts were removed with a cotton swab and the migrated cells on the distal side of the insert were fixed and stained with Hemacolor (EMD Chemicals, Inc., Gibbstown, NJ). To monitor invasive migration, similar procedures were carried out with the culture inserts (polyethylene terephthalate membrane with 8.0 μm pores #353097, BD Biosciences, Franklin Lakes, NJ), which were coated with rat-tail collagen, type 1 (BD Biosciences) as previously described 19 .…”

“…Immunoblot analyses with specific antibodies were carried out following our previously published procedures 19 . The following antibodies were used for immunoblot analyses.…”

“…Of the different G proteins that can be activated by LPA, the G proteins belonging to G12 family of heterotrimeric G proteins - defined by Gα 12 and Gα 13 -, are by far the most potent G proteins in transmitting oncogenic signals 16 . Gα 12 and Gα 13 , which are characterized as gep oncogenes 17-19 , have been shown to be involved in the activation of similar as well as distinct set of oncogenic pathways. While Gα 12 appears to be more involved in cell proliferation 19 , Gα 13 has been shown to be specifically involved in stimulating cell migration regulated by G protein coupled receptors as well as receptor tyrosine kinases 20-24 .…”

“…Gα 12 and Gα 13 , which are characterized as gep oncogenes 17-19 , have been shown to be involved in the activation of similar as well as distinct set of oncogenic pathways. While Gα 12 appears to be more involved in cell proliferation 19 , Gα 13 has been shown to be specifically involved in stimulating cell migration regulated by G protein coupled receptors as well as receptor tyrosine kinases 20-24 . Based on these correlates, it can be hypothesized that LPA-mediated metastatic migration of pancreatic cancer cells involves Gα 13 .…”

SPAG9 is overexpressed in osteosarcoma, and regulates cell proliferation and invasion through regulation of JunD

“…The current study observed negative SPAG9 staining in normal bone tissues, and positive cytoplasmic SPAG9 expression in 63.8% (37/58) of osteosarcoma tissues, which was consistent with previous studies (19,. A number of studies have described the role of SPAG9 in cancer cell proliferation and provided accumulating evidence that characterizes SPAG9 as an oncoprotein regulating cell invasion. It was reported that SPAG9 siRNA knockdown inhibited cell invasion and proliferation in renal, lung and colorectal carcinoma (13,21,(23)(24)(25). To gain insight into the function of SPAG9 in osteosarcoma progression, SPAG9 expression was knocked down in the U2OS cell line and upregulated in the MG63 cell line in the present study.…”