The Role of the UNC-82 Protein Kinase in Organizing Myosin Filaments in Striated Muscle of Caenorhabditis elegans

Abstract

We study the mechanisms that guide the formation and maintenance of the highly ordered actin-myosin cytoskeleton in striated muscle. The UNC-82 kinase of Caenorhabditis elegans is orthologous to mammalian kinases ARK5/NUAK1 and SNARK/ NUAK2. UNC-82 localizes to the M-line, and is required for proper organization of thick filaments, but its substrate and mechanism of action are unknown. Antibody staining of three mutants with missense mutations in the UNC-82 catalytic domain revealed muscle structure that is less disorganized than in the null unc-82(0), but contained distinctive ectopic accumulations not found in unc-82(0). These accumulations contain paramyosin and myosin B, but lack myosin A and myosin A-associated proteins, as well as proteins of the integrin-associated complex. Fluorescently tagged missense mutant protein UNC-82 E424K localized normally in wild type; however, in unc-82(0), the tagged protein was found in the ectopic accumulations, which we also show to label with recently synthesized paramyosin. Recruitment of wild-type UNC-82::GFP to aggregates of differing protein composition in five muscle-affecting mutants revealed that colocalization of UNC-82 and paramyosin does not require UNC-96, UNC-98/ZnF, UNC-89/obscurin, CSN-5, myosin A, or myosin B individually. Dosage effects in paramyosin mutants suggest that UNC-82 acts as part of a complex, in which its stoichiometric relationship with paramyosin is critical. UNC-82 dosage affects muscle organization in the absence of paramyosin, perhaps through myosin B. We present evidence that the interaction of UNC-98/ZnF with myosin A is independent of UNC-82, and that UNC-82 acts upstream of UNC-98/ZnF in a pathway that organizes paramyosin during thick filament assembly.

Role of ARK5 in cancer and other diseases (Review)

“…ARK5 knockout could lead to alterations in contractile apparatus protein (the actin-myosin cytoskeleton) phosphorylation and SNARK reduction may lead to muscle mass disruption with increasing age. These results revealed the conserved role of UNC-82/ARK5/SNARK in muscle generation across diverse animal lineages ( 27 ).…”

“…Uncordinated-82 (UNC-82) kinase serves a key role in Caenorhabditis elegans , a nematode, and is an orthologue of human ARK5 and SNF1/AMP kinase-regulated kinase (SNARK) that is necessary for myosin filament reorganization during cellular elongation ( 27 ). Research has suggested that ARK5 may exert a similar function to UNC-82 in striated muscle development ( 130 ).…”

“…A previous in vitro study has demonstrated that ARK5 expression is a key element in multiple myeloma invasion and metastasis and participates in these processes by modulating insulin-like growth factor (IGF)-1 expression (8). Schiller et al and Perumal et al (27,28) demonstrated that the ratio of AMP/ATP increased during energy deficiency, leading to phosphoric acid-dependent AMPK activation. Eventually, the level of ATP returned to normal due to the inhibition of energy-consuming pathways.…”