Myristoylated alanine-rich C kinase substrate protein and mRNA in bovine corpus luteum during the estrous cycle

The bovine corpus luteum contains a myristoylated alanine-rich C kinase substrate (MARCKS) protein known to crosslink actin filaments in the cytoskeletal cortex associated with the plasma membrane. We conducted experiments to determine whether concentrations of MARCKS mRNA and protein in the bovine corpus luteum varied during theestrous cycle. Using Northern blots probed with a MARCKS cDNA, we found that luteal concentrations of MARCKS mRNA were greatest on d 4, 8, and 12 and markedly reduced on d 16 of the cycle (p<0.08). Similarly, Western blot analysis of luteal proteins revealed that concentrations of MARCKS protein were greatest on d 8 and least on d 16 of the cycle (p<0.01). Exposure of slices from a d 8 corpus luteum to prostaglandin F_2α (PGF_2α) during a 10-min incubation in the presence of [³²P]-orthophosphate resulted in enhanced phosphorylation of MARCKS in membrane and cytosolic fractions compared to that of controls. We therefore concluded that expression of the luteal MARCKS protein gene may be regulated and that PGF_2α-induced phosphorylation of this protein is attributable to activation of protein kinase C.