Overexpression of progesterone receptor B increases sensitivity of human colon muscle cells to progesterone

Abstract

Colon muscle strips and cells from female patients with slow-transit constipation (STC) exhibit impaired motility, signal transduction abnormalities characterized by downregulation of Gq/11and upregulation of Gsproteins, decreased cyclooxygenase (COX)-1 and thromboxane (Tx)B2levels, increased COX-2 and PGE2levels, and overexpression of progesterone receptors (PGR). Progesterone (P4) treatment of normal cells reproduced these motility and signal transduction abnormalities. The purpose of the study was to examine whether overexpression of PGR-B reproduces these abnormalities by rendering the cells more sensitive to physiological concentrations of P4. Cultured human colon muscle was transfected with a plasmid DNA expressing PGR-B. The mRNAs of PGR, COX-1, COX-2, and Gq/11were determined by quantitative real-time PCR. Their protein expression was determined by Western blot, and prostaglandins were measured by radioimmunoassay. Cultured muscle cells maintained their phenotypic features determined with myosin light chain (MLC) and h-caldesmon antibodies. Control and transfected muscle cells responded to 10−6M P4. In contrast, muscle cells transfected with PGR-B responded to lower P4concentration (10−7M). This P4concentration reduced MLC phosphorylation induced by CCK-8 (10−8M), downregulated Gq/11, and decreased COX-1 and TxB2levels. It upregulated Gsproteins. It also increased COX-2 and PGE2levels. We conclude that overexpression of PGR-B renders the cells more sensitive to physiological concentrations of P4. These results are consistent with the hypothesis that overexpression of PGR-B contributes to the motility and signal transduction abnormalities observed in female patients with STC and normal serum levels of P4.