Rabbit Anti-Human MARK2 (Phospho-Thr596) polyclonal antibody

MAP/Microtubule affinity-regulating kinase 4 (MARK4), a Ser/Thr protein kinases, is related to the Par-1 (partitioning-defective) gene products, and is the human ortholog of Par-1. MARK4 shows its role in the cell polarity at the time of embryonic development. It is mostly located at the basal region of cells, providing apico-basal polarity. Here, we made two variants of human Par-1d (MARK4), kinase domain (MARK4-F2), and kinase domain along with 59 N-terminal residues (MARK4-F1) and saw their ATPase hydrolysis in the presence of each other. We observed that the activity of one variant was increased in the presence of other. We also demonstrated that both variants were phosphorylated by atypical PKC and their activities were increased in the presence of increasing concentration of atypical protein kinase c (aPKC). The phosphorylation was observed at the serine and threonine residues of MARK4. The interaction of MARK2 and MARK3 with aPKC and their negative regulation by aPKC is already known. This study confirms a functional link between aPKC and MARK4, two central determinants of cell polarity, and it suggests that aPKC may regulate all four members of Par-1 through phosphorylating them in polarized cells.

The microtubule cytoskeleton is differentially regulated by a diverse array of proteins during interphase and mitosis. Op18/stathmin (Op18) and microtubule-associated protein (MAP)4 have been ascribed opposite general microtubule-directed activities, namely, microtubule destabilization and stabilization, respectively, both of which can be inhibited by phosphorylation. Here, using three human cell models, we depleted cells of Op18 and/or MAP4 by expression of interfering hairpin RNAs and we analyzed the resulting phenotypes. We found that the endogenous levels of Op18 and MAP4 have opposite and counteractive activities that largely govern the partitioning of tubulin dimers in the microtubule array at interphase. Op18 and MAP4 were also found to be the downstream targets of Ca2+- and calmodulin-dependent protein kinase IV and PAR-1/MARK2 kinase, respectively, that control the demonstrated counteractive phosphorylation-mediated regulation of tubulin dimer partitioning. Furthermore, to address mechanisms regulating microtubule polymerization in response to cell signals, we developed a system for inducible gene product replacement. This approach revealed that site-specific phosphorylation of Op18 is both necessary and sufficient for polymerization of microtubules in response to the multifaceted signaling event of stimulation of the T cell antigen receptor complex, which activates several signal transduction pathways.