A-kinase anchoring protein 13 interacts with the vitamin D receptor to alter vitamin D-dependent gene activation in uterine leiomyoma cells

Abstract

Abstract Objective To determine if AKAP13 interacts with the VDR to alter vitamin D-dependent signaling in fibroid cells. Uterine leiomyoma (fibroids) are characterized by a fibrotic extracellular matrix (ECM) and are associated with vitamin D deficiency. Treatment with vitamin D (1,25-dihydroxyvitamin D3) reduced fibroid growth and ECM gene expression. A-kinase Anchoring Protein 13 (AKAP13) is overexpressed in fibroids and interacts with nuclear hormone receptors, but it is not known whether AKAP13 might interact with the vitamin D receptor (VDR) to affect vitamin D signaling in fibroids. Design Laboratory studies. Setting Translational science laboratory. Interventions Human immortalized fibroid or myometrial cells were treated with 1,25-hydroxyvitamin D3 (1,25(OH)2D3) and transfected using expression constructs for AKAP13 or AKAP13 mutants, RhoQL, C3 transferase, or small interfering RNAs (siRNA). Main Outcome Measure(s): mRNA levels of AKAP13, fibromodulin, and versican as measured by quantitative real-time PCR (qPCR). GST-binding assays. Vitamin D-dependent gene activation as measured by luciferase assays. Results 1,25(OH)2D3 resulted in a significant reduction in mRNA levels encoding AKAP13, versican, and fibromodulin. siRNA silencing of AKAP13 decreased both fibromodulin and versican mRNA levels. GST-binding assays revealed that AKAP13 bound to the VDR through its nuclear receptor interacting region. Cotransfection of AKAP13 and VDR significantly reduced vitamin D-dependent gene activation. RhoA pathway inhibition partially relieved repression of vitamin D-dependent gene activation by AKAP13. Conclusions These data suggest that AKAP13 inhibited the vitamin D receptor activation by a mechanism that required, at least in part, RhoA activation.