A novel isoform of sarcolemmal membrane-associated protein (SLMAP) is a component of the microtubule organizing centre

Abstract

The microtubule organizing centre (MTOC) or the centrosome serves a crucial role in the establishment of cellular polarity, organization of interphase microtubules and the formation of the bipolar mitotic spindle. We have elucidated the genomic structure of a gene encoding the sarcolemmal membrane-associated protein (SLMAP), which encodes a 91 kDa polypeptide with a previously uncharacterized N-terminal sequence encompassing a forkhead-associated (FHA) domain that resides at the centrosome. Anti-peptide antibodies directed against SLMAP N-terminal sequences showed colocalization with γ-tubulin at the centrosomes at all phases of the cell cycle. Agents that specifically disrupt microtubules did not affect SLMAP association with centrosomes. Furthermore, SLMAP sequences directed a reporter green fluorescent protein (GFP) to the centrosome, and deletions of the newly identified N-terminal sequence from SLMAP prevented the centrosomal targeting. Deletion-mutant analysis concluded that overall, structural determinants in SLMAP were responsible for centrosomal targeting. Elevated levels of centrosomal SLMAP were found to be lethal, whereas mutants that lacked centrosomal targeting inhibited cell growth accompanied by an accumulation of cells at the G2/M phase of the cell cycle.

Tiered Assembly of the Yeast Far3-7-8-9-10-11 Complex at the Endoplasmic Reticulum

“…Consistent with their localization, the STRIPAK complex from these two species has been reported to play roles in mitosis (9,12,20). Our failure to detect localization of the yeast Far complex components and even the Far9 truncation mutant without its tail-anchor domain to the spindle pole body is consistent with the hypothesis of Frost et al (9) that the function of the STRIPAK complex may have been "repurposed" and the S. cerevisiae STRIPAK complex has lost its function in mitosis.…”

“…Human SLMAP and the S. pombe STRIPAK complex also localize to the centrosome and the spindle pole body, respectively (9,12,20). Consistent with their localization, the STRIPAK complex from these two species has been reported to play roles in mitosis (9,12,20).…”

“…The SLMAP gene has several splice variants, encoding tail-anchored membrane proteins that associate with the sarcolemmal membrane in muscle cells, the endoplasmic reticulum and the mitochondrial membrane in nonmuscle cells, and the centrosome and the outer nuclear envelope (9 -13). SLMAP is required for myoblast fusion, centrosome function, and structural arrangement of the excitation-contraction coupling apparatus in cardiomyocytes (9,12,14,15). Much remains to be determined about the role of the STRIPAK components, the mechanism of their regulation, and the identity of their substrates.…”

HectD1 E3 Ligase Modifies Adenomatous Polyposis Coli (APC) with Polyubiquitin to Promote the APC-Axin Interaction

“…1B). These Trabid-interacting proteins are known components of the STRIPAK (Striatin-interacting phosphatase and kinase) complex and include the Striatin family of WD40 domain proteins that function as regulatory subunits of protein phosphatase PP2A; factors that regulate cortical actin cytoskeleton dynamics: cortactin-binding protein 2, CTTNBP2NL, and FAM40A; and the centrosome-associated protein SLMAP (32)(33)(34). Interestingly, we did not find any PP2A subunits in the Trabid IPs, suggesting mutually exclusive or transient association of subcomplexes of STRIPAK to Trabid and PP2A (33).…”

Deficiency in Kelch protein Klhl31 causes congenital myopathy in mice

“…To test this and to further validate our antibody, we also transfected COS-7 cells with a myc- phosphatase and kinase (STRIPAK) complex, which has been described as possessing roles in multiple cellular processes, including signaling, trafficking, cell migration, and cardiac function (18). Previous reports have shown that Slmap is involved in microtubule organization (19), myoblast fusion (20), and excitation-contraction coupling (21). It has also been reported that mutations in SLMAP may give rise to Brugada syndrome (22).…”