Hypothetical schematic model for the regulation of claudin-2 expression in MDCK cells.

<p>GATA-4 is required for optimal transcription of claudin-2 (and other TJ proteins, not shown for simplicity) (double arrow in scheme). Cingulin and paracingulin redundantly control the mRNA and protein expression of GATA-4, and independently contribute to the down-regulation of active RhoA in confluent cells. Active RhoA increases claudin-2 expression, either through GATA-4, and/or other, unknown mechanisms (question marks), but is ineffective when GATA-4 is down-regulated.