α3β1 Integrin Suppresses Prostate Cancer Metastasis via Regulation of the Hippo Pathway

Abstract

Existing anti-cancer strategies focused on disrupting integrin functions in tumor cells or tumor-involved endothelial cells have met limited success. An alternative strategy is to augment integrin-mediated pathways that suppress tumor progression, but how integrins can signal to restrain malignant behavior remains unclear. To address this issue, we generated an in vivo model of prostate cancer metastasis via depletion of α3β1 integrin, a correlation observed in a significant proportion of prostate cancers. Our data describe a mechanism whereby α3β1 signals through Abl family kinases to restrain Rho GTPase activity, support Hippo pathway suppressor functions, and restrain prostate cancer migration, invasion, and anchorage-independent growth. This α3β1-Abl kinase-Hippo suppressor pathway identified α3 integrin-deficient prostate cancers as potential candidates for Hippo-targeted therapies currently under development, suggesting new strategies for targeting metastatic prostate cancer based on integrin expression. Our data also revealed paradoxical tumor suppressor functions for Abl kinases in prostate cancer that may help to explain the failure of Abl kinase inhibitor imatinib in prostate cancer clinical trials.

Enabling Tumor Growth and Progression: Recent Progress in Unraveling the Functions of ABL Kinases in Solid Tumor Cells

“…For example, upregulation of miR-20a in aggressive prostate cancers promotes migration and invasion of PC-3/DU145 cells by inhibiting ABL2 expression [83]. Likewise, depletion of integrin α3β1 increases RHOA/YAP/TAZ activation and prostate cancer invasion/metastasis by inhibiting ABL1/ABL2 signaling [123]. Similarly, although ABL1 activation promotes invasion in some GBM models [52], permanent silencing of ABL1 in PC-3 cells increases invasiveness, although it also simultaneously inhibits proliferation, tumor growth, and stem cell features [67].…”

Cancer cells resist mechanical destruction in the circulation via RhoA-myosin II axis

“…To test whether inhibition of myosin II can affect the survival of CTCs over a longer period of time in a mouse model of metastasis, we employed an orthotopic model of metastatic prostate cancer that we had previously developed 33 . Utilizing this model, we treated tumor bearing mice with a single dose of blebbistatin (2.5 mg/kg) and measured CTC number in cardiac blood 3 hours later ( Figure 5A).…”

“…Immediately following FSS, we fixed cells with 1% paraformaldehyde for 20 min. After washing with PBS, cells were stained with 1: Orthotopic prostate xenograft model: 5x10 4 GS689.Li cells were orthotopically injected into the anterior prostate lobe of [8][9][10][11][12][13] week-old NSG mice as described previously 49 . As described above, this cell line was derived from the PC-3 parent line by selection for cells that are highly metastatic in vivo 45 .…”

Abl kinase deficiency promotes AKT pathway activation and prostate cancer progression and metastasis

“…fluorescence microscopy using an Olympus SZX12 stereomicroscope, as described [33]. with 5 mg/mL BSA, glutamine, penicillin/streptomycin, non-essential amino acids, 25 mM 4 HEPES pH 7.2, and insulin-transferrin-selenium (ITS)] on 35-mm dishes coated with 10 ug/mL 5 rat tail collagen I. Time-lapse images were acquired as described previously [33], and migration 6 speed and displacement were calculated using the mTrackJ plugin [35].…”

“…fluorescence microscopy using an Olympus SZX12 stereomicroscope, as described [33]. with 5 mg/mL BSA, glutamine, penicillin/streptomycin, non-essential amino acids, 25 mM 4 HEPES pH 7.2, and insulin-transferrin-selenium (ITS)] on 35-mm dishes coated with 10 ug/mL 5 rat tail collagen I. Time-lapse images were acquired as described previously [33], and migration 6 speed and displacement were calculated using the mTrackJ plugin [35]. ImageJ software was 7 used to measure the morphological characteristics of migrating cells (at t = 20 minutes) by 8 making cell traces using the Freehand selections tool, followed by the Measure (Shape We previously described the isolation of GS689.Li cells, a metastatic variant of the PC-3 10 prostate carcinoma [34].…”