• Regulation of Intracellular Trafficking of Laminin Binding Integrins in Prostate Cancer

      Cress, Anne E.; Das, Lipsa; Cress, Anne E.; Martinez, Jesse D.; Wilson, Jean M.; Laukaitis, Christina; Nagle, Raymond B.; Knudsen, Beatrice S. (The University of Arizona., 2017)
      Laminin binding integrins (α6β1 and α3β1) are persistently but differentially expressed throughout prostate cancer progression and metastasis. Prostate cancer primarily invades through laminin rich nerve for extracapsular escape during cancer metastasis. An intense expression of the pro-metastatic α6 integrin was observed during perineural invasion with a heterogeneous distribution of the integrin on the cancer cell membrane as well as intracellularly. Bone and soft tissue metastasis of human prostate cancer demonstrated a similar pattern where 75-80% of the cancers had significant intracellular staining. This was correlated with an mRNA overexpression of various intracellular trafficking regulators. Using a prostate cancer cell culture model of DU145 cells, the α6 integrin was found to be constitutively internalized in cancer cells at a rate of 3.25 min-1, which was 3 fold greater than internalization rate of α3 integrin, classically considered a "non-circulating" receptor. α6 and α3 integrins function coordinately to regulate cell migration during development, wound healing. Their orchestrated redistribution during these processes is well-known, but the mechanism remains elusive. Current study identifies intracellular trafficking of these integrins as a key mechanism of their coordination. Depletion of α3 integrin in prostate cancer cells significantly increased internalization of α6 integrin up to 1.7-fold and increased localization of α6 integrin at cell-cell membrane locations. There was a concomitant 1.8-fold increase in cell migration significantly dependent on α6 integrin. Depletion of α6 integrin expression however, had no effects on the internalization of α3 integrin indicating that the identified coordination was unidirectional. α6 integrin trafficking drives cancer invasion, but its selective regulators are unknown. Here, Rab11FIP5 was identified as a selective regulator of α6 integrin recycling to cell membrane. Interestingly, α6 integrin was found to be primarily recycled to the cell-cell membranes where it colocalized with Rab11 and Rab11FIP5. Depletion of Rab11FIP5 reduced such membrane expression of α6 integrin, inhibited cell-cell cohesion in 3D culture and significantly reduced cell migration. The localization of α6 and α3 integrin at these locations have been implicated in cell adhesion. Based on current study α6 recycling by Rab11FIP5 might be key to such function. Another Rab11 effector protein Rab11FIP1 was identified as a regulator of both α3 and α6 integrin trafficking. Depletion of Rab11FIP1 reduced membrane expression of α3 integrin by significantly increasing its internalization and reducing the recycling. There was a major effect on α6 integrin internalization, which increased to an extent similar to that observed on α3 integrin depletion. Rab11FIP1 regulated α6 integrin recycling, in a pathway found to be independent of Rab11FIP5. Taken together, current research defined Rab11FIPs as regulators of α6 and α3 integrins. A unidirectional coordination between α6 and α3 integrin was identified such that loss of α3 integrin, representative of high grade prostate cancer, amplifies integrin α6 integrin internalization and a resultant migratory phenotype.