Estrogen Activation of CaM Kinases and Transcription Is Blocked by Vitamin D in MCF-7 Breast Cancer Cells

Abstract

Abstract. Calcium/calmodulin-dependent protein kinase (CaM Kinase) proteins are targets of hormones and growth factors and regulate cancer cell growth, apoptosis and migration. The hormone estrogen (E2) utilizes CaM Kinases to activate the Extracellular-signal regulated kinase (ERK) leading to MCF-7 breast cancer cell growth. The hormone Vitamin D (Vit D) may inhibit breast cancer cell growth however the cellular mechanisms of Vit D action remain to be elucidated. Within the present study we provide data that E2 stimulation of MCF-7 cells activates CaM Kinase Kinase (CaM KK), CaM KI, and ERK and the transcription factors Elk-1 and SRF. E2 treatment of MCF-7 cells potently stimulated Elk-1/SRF directed transcription of SRE-luciferase reporters. E2 activation of ERK, Elk-1, SRF and SRE-dependent luciferase activities were blocked by treating cells with the CaM KK inhibitor, STO-609, and the ERK inhibitor, U0126. Moreover, siRNAs directed against CaM KK and ERK blocked transcription factor phosphorylation and luciferase activity. Treatment of cells with Vit D, the hormone Epinephrine (Epi), or Forskolin, prevented E2 activation of CaM KK and ERK. Interestingly, Vit D promoted a PKA-dependent phosphorylation and inhibition of CaM KK as well as its association with 14-3-3. Epi and Vit D treatment of cells blocked the ability of E2 to active Elk-1 and SRE-luciferase activity. This data suggests an important role for CaM KK and ERK in regulating transcription downstream of E2 in MCF-7 cells. Our results also suggest that Vit D treatment of MCF-7 cells utilizes a unique PKA-dependent mechanism to block E2 activation of CaM KK, ERK and transcription.