Myomasp/LRRC39, a heart- and muscle-specific protein, is a novel component of the sarcomeric M-band and is involved in stretch sensing.
OBJECTIVE
The M-band represents a transverse structure in the center of the sarcomeric A-band and provides an anchor for the myosin-containing thick filaments. In contrast to other sarcomeric structures, eg, the Z-disc, only few M-band-specific proteins have been identified to date, and its exact molecular composition remains unclear.


RESULTS
Using a bioinformatic approach to identify novel heart- and muscle-specific genes, we found a leucine rich protein, myomasp (Myosin-interacting, M-band-associated stress-responsive protein)/LRRC39. RT-PCR and Northern and Western blot analyses confirmed a cardiac-enriched expression pattern, and immunolocalization of myomasp revealed a strong and specific signal at the sarcomeric M-band. Yeast 2-hybrid screens, as well as coimmunoprecipitation experiments, identified the C terminus of myosin heavy chain (MYH)7 as an interaction partner for myomasp. Knockdown of myomasp in neonatal rat ventricular myocytes (NRVCMs) led to a significant upregulation of the stretch-sensitive genes GDF-15 and BNP. Conversely, the expression of MYH7 and the M-band proteins myomesin-1 and -2 was found to be markedly reduced. Mechanistically, knockdown of myomasp in NRVCM led to a dose-dependent suppression of serum response factor-dependent gene expression, consistent with earlier observations linking the M-band to serum response factor-mediated signaling. Finally, downregulation of myomasp/LRRC39 in spontaneously beating engineered heart tissue constructs resulted in significantly lower force generation and reduced fractional shortening. Likewise, knockdown of the myomasp/LRRC39 ortholog in zebrafish resulted in severely impaired heart function and cardiomyopathy in vivo.


CONCLUSIONS
These findings reveal myomasp as a previously unrecognized component of an M-band-associated signaling pathway that regulates cardiomyocyte gene expression in response to biomechanical stress.
Will
Rainer D
RD
Department of Internal Medicine III, University of Heidelberg, Germany.
Eden
Matthias
M
Just
Steffen
S
Hansen
Arne
A
Eder
Alexandra
A
Frank
Derk
D
Kuhn
Christian
C
Seeger
Thalia S
TS
Oehl
Ulrike
U
Wiemann
Stefan
S
Korn
Bernhard
B
Koegl
Manfred
M
Rottbauer
Wolfgang
W
Eschenhagen
Thomas
T
Katus
Hugo A
HA
Frey
Norbert
N
D000595:Amino Acid Sequence; D000818:Animals; D000831:Animals, Newborn; D015152:Blotting, Northern; D015153:Blotting, Western; D024722:Cardiac Myosins / Q000378:metabolism; D009202:Cardiomyopathies / Q000235:genetics / Q000378:metabolism / Q000503:physiopathology; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D003001:Cloning, Molecular; D064211:Connectin; D004625:Embryo, Nonmammalian / Q000378:metabolism; D020869:Gene Expression Profiling / Q000379:methods; D005786:Gene Expression Regulation; D055436:Growth Differentiation Factor 15 / Q000378:metabolism; D006801:Humans; D007150:Immunohistochemistry; D047468:Immunoprecipitation; D000090263:Leucine-Rich Repeat Proteins; D008297:Male; D040542:Mechanotransduction, Cellular; D051379:Mice; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D009124:Muscle Proteins / Q000235:genetics / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000378:metabolism; D009200:Myocardial Contraction; D032383:Myocytes, Cardiac / Q000378:metabolism*; D018995:Myosin Heavy Chains / Q000378:metabolism; D020097:Natriuretic Peptide, Brain / Q000378:metabolism; D020411:Oligonucleotide Array Sequence Analysis; D054730:Protein Interaction Domains and Motifs; D025941:Protein Interaction Mapping; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D051381:Rats; D017207:Rats, Sprague-Dawley; D017208:Rats, Wistar; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012518:Sarcomeres / Q000378:metabolism*; D026362:Serum Response Factor / Q000378:metabolism; D013314:Stress, Mechanical; D014162:Transfection; D020798:Two-Hybrid System Techniques; D015027:Zebrafish
D002352:Carrier Proteins; D064211:Connectin; D055436:Growth Differentiation Factor 15; C554140:LRRC39 protein, human; C554139:LRRC39 protein, mouse; D000090263:Leucine-Rich Repeat Proteins; C501641:MYH7 protein, human; D009124:Muscle Proteins; C577286:Myom1 protein, rat; D011506:Proteins; D026362:Serum Response Factor; D020097:Natriuretic Peptide, Brain; D024722:Cardiac Myosins; D018995:Myosin Heavy Chains