Regulated synthesis and functions of laminin 5 in polarized madin-darby canine kidney epithelial cells.

Renal tubular epithelial cells synthesize laminin (LN)5 during regeneration of the epithelium after ischemic injury. LN5 is a truncated laminin isoform of particular importance in the epidermis, but it is also constitutively expressed in a number of other epithelia. To investigate the role of LN5 in morphogenesis of a simple renal epithelium, we examined the synthesis and function of LN5 in the spreading, proliferation, wound-edge migration, and apical-basal polarization of Madin-Darby canine kidney (MDCK) cells. MDCK cells synthesize LN5 only when subconfluent, and they degrade the existing LN5 matrix when confluent. Through the use of small-interfering RNA to knockdown the LN5 alpha3 subunit, we were able to demonstrate that LN5 is necessary for cell proliferation and efficient wound-edge migration, but not apical-basal polarization. Surprisingly, suppression of LN5 production caused cells to spread much more extensively than normal on uncoated surfaces, and exogenous keratinocyte LN5 was unable to rescue this phenotype. MDCK cells also synthesized laminin alpha5, a component of LN10, that independent studies suggest may form an assembled basal lamina important for polarization. Overall, our findings indicate that LN5 is likely to play an important role in regulating cell spreading, migration, and proliferation during reconstitution of a continuous epithelium.