The stem cell factor (SCF) binds to c-Kit in endothelial cells, thus activating downstream signaling and angiogenesis. Herein, we examined the role of G protein subunit alpha inhibitory (Gαi) proteins in this process. In MEFs and HUVECs, Gαi1/3 was associated with SCF-activated c-Kit, promoting c-Kit endocytosis, and binding of key adaptor proteins, subsequently transducing downstream signaling. SCF-induced Akt-mTOR and Erk activation was robustly attenuated by Gαi1/3 silencing or knockout (KO), or due to dominant negative mutations but was strengthened substantially following ectopic overexpression of Gαi1/3. SCF-induced HUVEC proliferation, migration, and capillary tube formation were suppressed after Gαi1/3 silencing or KO, or due to dominant negative mutations. In vivo , endothelial knockdown of Gαi1/3 by intravitreous injection of endothelial-specific shRNA adeno-associated virus (AAV) potently reduced SCF-induced signaling and retinal angiogenesis in mice. Moreover, mRNA and protein expressions of SCF increased significantly in the retinal tissues of streptozotocin-induced diabetic retinopathy (DR) mice. SCF silencing, through intravitreous injection of SCF shRNA AAV, inhibited pathological retinal angiogenesis and degeneration of retinal ganglion cells in DR mice. Finally, the expression of SCF and c-Kit increased in proliferative retinal tissues of human patients with proliferative DR. Taken together, Gαi1/3 mediate SCF/c-Kit-activated signaling and angiogenesis.
Pancreatic cancer has an extremely poor prognosis. Here we examined expression, potential functions and underlying mechanisms of MXRA5 (matrix remodeling associated 5) in pancreatic cancer. Bioinformatics studies revealed that MXRA5 transcripts are significantly elevated in pancreatic cancer tissues, correlating with the poor overall survival, high T-stage, N1 and pathologic stage of the patients. MXRA5 mRNA and protein expression is significantly elevated in microarray pancreatic cancer tissues and different pancreatic cancer cells. In primary and immortalized (BxPC-3 and PANC-1 lines) pancreatic cancer cells, shRNA-induced MXRA5 silencing or CRISPR/Cas9-mediated MXRA5 knockout suppressed cell survival, proliferation, migration, invasion, and epithelial-mesenchymal transition (EMT), while provoking cell apoptosis. Conversely, forced overexpression of MXRA5 further promoted pancreatic cancer cell progression and EMT. Bioinformatics studies and the protein chip analyses revealed that differentially expressed genes (DEGs) and differentially expressed proteins (DEPs) in MXRA5-overexpressed primary pancreatic cancer cells were enriched in the PI3K-Akt-mTOR cascade. Indeed, Akt-mTOR activation in primary human pancreatic cancer cells was inhibited by MXRA5 shRNA or knockout, but was augmented following MXRA5 overexpression. In vivo, the growth of MXRA5 KO PANC-1 xenografts was largely inhibited in nude mice. Moreover, intratumoral injection of adeno-associated virus-packed MXRA5 shRNA potently inhibited primary pancreatic cancer cell growth in nude mice. Akt-mTOR activation was also largely inhibited in the MXRA5-depleted pancreatic cancer xenografts. Contrarily MXRA5 overexpression promoted primary pancreatic cancer cell growth in nude mice. Together, overexpressed MXRA5 is important for pancreatic cancer cell growth possibly through promoting EMT and Akt-mTOR activation. MXRA5 could be a potential therapeutic oncotarget for pancreatic cancer.
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