Dynamic integrin expression, atypical nuclear localization, and spatial distribution during ovarian cancer...

Aggregation and adhesion of ovarian cancer cells are facilitated by integrins, key adhesion receptors in ovarian cancer. Here we identify changes in the expression of integrins (ITG), their ligands and regulators during ovarian cancer progression and metastatic dissemination that allow for the adaptation of the cellular phenotype to aggregation and adhesion and promote cancer cell survival and metastatic outgrowth.

We mimicked the stages of peritoneal dissemination of ovarian metastases by using benign cells and ovarian cancer cells representing slow- and fast developing disease and generated adherent, spheroid, and adherent-spheroid mouse ovarian surface epithelial cultures adjusted for oxygen and glucose levels as reported for malignant ascites. We determined changes in integrin expression, other adhesion receptors, ECM proteins and their regulators by qPCR RT2 PCR arrays and Western blotting. Spatial and intracellular protein expression in 3D spheroids was determined by confocal microscopy and quantitated by IMARIS software. Relevance of specific integrins for aggregation, adherence, and outgrowth was determined using specific inhibitors.

Small changes in the highly expressed ITGα3, ITGα5, ITGαV, and ITGβ1 after aggregation in concert with elevated ITGα4 and ITGα5 expression suggested changes in integrin heterodimer composition that support aggregation. 3D spatial analysis of adherent spheroids revealed high expression of ITGα2, ITGαV, and ITGβ1 at the adhesion sites, while ITGα3 was predominantly expressed in the spheroid periphery. This was not correlated to their distinct spatial expression patterns in spheroids (uniformly expressed or higher at the periphery). Importantly, most integrins and CD44 were localized in the nucleus where they potentially can affect gene transcription. Only the inhibition of ITGαVβ1 and ITGα2β1 effectively suppressed spheroid adhesion and outgrowth, highlighting their importance as stage-specific target to block peritoneal metastasis.

Our studies show that integrin expression and localization are dynamic, spatially regulated, and functionally compartmentalized during ovarian cancer progression and dissemination. The coordinated upregulation of integrins, other adhesion molecules (CD44, NCAM1, VCAM), ECM (FN1, collagens) and their regulators (SPP1, TIMP2,3) in response to the culture conditions indicate a complex reprogramming of adhesion networks that can facilitate different steps of ovarian cancer progression and dissemination. Nuclear localization of integrins and CD44 point to dual roles in adhesion, survival, and proliferation by activating adhesion-mediated signaling pathways and directly affect gene transcription that support a switch from a more dormant phenotype to active proliferation and invasion after adhesion.