What is the detailed mechanism of PMA differentiation of U937 cells?

Treating U937 (cell line of human myeloid leukemia) cells with PMA (phorbol 12-myristate 13-aceate) has been shown to activate RhoA, a GTPase protein. The activation of RhoA increases ROCK1 and ROCK2 expression, as well as MYPT1 phosphorylation. Suppression of the RhoA/ROCK signaling pathway inhibits macrophage differentiation, evident by the decreased expression of CD68 and SR-A, both of which are expressed by macrophages.