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 sub strate (MARCKS) protein known to crosslink actin filaments in the cytoskele tal 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 the estrous 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 co ncentrations of MARCKS protein were greatest on d 8 and least on d -16 of t he cycle (p < 0.01). Exposure of slices from a d 8 corpus luteum to prostag landin F-2 alpha (PGF(2 alpha)) during a 10-min incubation in the presence of [P-32]-ortho-phosphate resulted in enhanced phosphorylation of MARCKS in membrane and cytosolic fractions compared to that of controls, We therefor e concluded that expression of the luteal MARCKS protein gene may be regula ted and that PGF(2 alpha)-induced phosphorylation of this protein is attrib utable to activation of protein kinase C.