SLMAP

SLMAP is a tail-anchored membrane protein expressed as multiple alternatively spliced isoforms whose distinct C-terminal transmembrane anchors dictate differential subcellular targeting, with the hydrophobicity of the tail anchor determining whether the protein localizes to the ER alone (TA1) or additionally to mitochondria (TA2) (PMID:19538755). An N-terminal FHA domain directs a 91 kDa isoform to the centrosome throughout the cell cycle, where dysregulated levels are lethal or arrest cells at G2/M (PMID:15126628), and the conserved FHA domain mediates incorporation into the STRIPAK complex, as shown for the fungal ortholog PRO45 which binds STRIPAK subunits and depends on them for nuclear-envelope targeting (PMID:25527523). In cardiac muscle SLMAP isoforms self-assemble and target sarcolemmal, T-tubule, and sarcoplasmic-reticulum membranes involved in excitation-contraction coupling (PMID:15591093); SLMAP regulates E-C coupling at the SR by controlling expression of calcium-cycling proteins and intracellular calcium transients, with cardiac overexpression causing SR/ER dilation, reduced ryanodine receptor/Ca2+-ATPase/calsequestrin/triadin levels, impaired contractility, and QT prolongation (PMID:22180652), and with the SLMAP-3 isoform interacting with striatin to modulate calcium transients and contractile rate (PMID:30856349). Through STRIPAK-linked signaling, SLMAP acts upstream of MST3 kinase to promote YAP activation in gut mesenchyme, supporting intestinal epithelial proliferation and proper gut length (PMID:40521668). SLMAP additionally associates with GLUT-4 in adipocytes to influence glucose uptake (PMID:21785580), and its expression is post-transcriptionally repressed by miR-29b-3p downstream of GLP-1 receptor signaling (PMID:36936522).

1. 2004 Medium

   Established that an FHA-domain-containing SLMAP isoform is a cell-cycle-relevant centrosomal protein, linking SLMAP to MTOC function and mitotic progression.

   Evidence Anti-peptide immunofluorescence, GFP-reporter targeting and deletion mapping, cell cycle profiling in cultured cells

   PMID:15126628

   Open questions at the time

   • Molecular function of SLMAP at the centrosome not defined
   • No partner identified mediating centrosomal targeting beyond the N-terminal sequence
   • Mechanism of G2/M arrest unexplained
2. 2004 Medium

   Showed SLMAP isoforms self-assemble and bind myosin and partition to distinct E-C coupling membranes, framing SLMAP as a membrane-targeted structural component of cardiac muscle.

   Evidence Co-immunoprecipitation/pulldown, subcellular fractionation and immunolocalization in cardiac myocytes

   PMID:15591093

   Open questions at the time

   • Myosin interaction rests on single Co-IP/pulldown without reciprocal validation
   • Functional consequence of homodimerization not tested
   • Which isoform binds myosin unclear
3. 2009 High

   Defined the biophysical rule for SLMAP isoform targeting, demonstrating that tail-anchor hydrophobicity selects between ER-only and ER-plus-mitochondrial localization.

   Evidence GFP-fusion targeting assays with site-directed mutagenesis of the tail-anchor transmembrane domain and confocal microscopy

   PMID:19538755

   Open questions at the time

   • Insertion machinery for the tail anchor not identified
   • Functional role of mitochondrial-targeted SLMAP not addressed
   • Targeting tested with reporter fusions, not endogenous isoforms
4. 2011 High

   Provided in vivo proof that SLMAP controls cardiac E-C coupling by regulating SR calcium-cycling protein expression and calcium handling.

   Evidence Cardiac-specific transgenic mice with electrophysiology (ECG), pressure monitoring, calcium uptake assays, fractionation, and imaging

   PMID:22180652

   Open questions at the time

   • Mechanism by which SLMAP controls calcium-protein expression unknown
   • Effect is from a gain-of-function/mistargeting construct rather than endogenous loss
   • Direct molecular targets at the SR not identified
5. 2011 Medium

   Connected SLMAP to metabolic regulation by linking a 45 kDa isoform to GLUT-4 and glucose uptake in adipocytes.

   Evidence Co-immunoprecipitation with GLUT-4 and siRNA knockdown with glucose uptake assay in adipocytes

   PMID:21785580

   Open questions at the time

   • GLUT-4 interaction from single Co-IP without reciprocal validation
   • Direct role in vesicle fusion/translocation not demonstrated
   • Relationship to other SLMAP isoforms/functions unclear
6. 2014 Medium

   Established the FHA-domain-dependent association of the SLMAP ortholog with the STRIPAK complex and its requirement for STRIPAK-dependent nuclear-envelope targeting and developmental processes.

   Evidence Superresolution SIM microscopy, yeast two-hybrid/pulldown, and genetic deletion/complementation in Sordaria macrospora

   PMID:25527523

   Open questions at the time

   • Demonstrated in fungal ortholog; mammalian STRIPAK linkage inferred
   • FHA-domain binding partners in the complex not fully mapped
   • Mechanistic link between localization and fusion phenotype unresolved
7. 2019 Medium

   Identified striatin as a cardiomyocyte SLMAP-3 partner and tied SLMAP levels to calcium transients and contractile rate, reinforcing its role in cardiac function.

   Evidence Proteomics interaction discovery with AAV overexpression/knockdown, live calcium imaging and contractile rate measurement

   PMID:30856349

   Open questions at the time

   • Striatin interaction from proteomics not orthogonally confirmed
   • Causal chain from STRN binding to calcium handling unmapped
   • Relationship to STRIPAK signaling in heart untested
8. 2023 Medium

   Placed SLMAP downstream of GLP-1R signaling by identifying miR-29b-3p as a direct repressor of SLMAP mRNA in cardiomyocytes.

   Evidence Dual-luciferase reporter assay, Western blot, qRT-PCR, and pharmacological GLP-1R inhibition

   PMID:36936522

   Open questions at the time

   • Downstream cardiac consequence of SLMAP repression not functionally dissected
   • Which SLMAP isoform is targeted unclear
   • Physiological relevance of the axis in vivo not established
9. 2025 High

   Defined SLMAP as an upstream regulator of MST3 in the YAP pathway controlling intestinal mesenchymal-epithelial signaling and gut growth.

   Evidence Mesenchyme-specific conditional knockout mice, Slmap;Mst3 double-mutant genetic epistasis, scRNA-seq, YAP activity and proliferation assays

   PMID:40521668

   Open questions at the time

   • Biochemical mechanism by which SLMAP inhibits MST3 not resolved
   • Role of STRIPAK in this regulation not directly tested
   • Partial rescue indicates additional MST3-independent effectors

• How SLMAP's shared FHA/STRIPAK module is mechanistically coupled to its diverse isoform-specific outputs (centrosome, cardiac SR calcium handling, GLUT-4, MST3/YAP) remains unresolved.
• No structural model of FHA-domain partner engagement
• Direct enzymatic or scaffold mechanism toward MST3 undefined
• Unifying principle linking tail-anchor targeting to downstream signaling absent