Differential expressions of myosin heavy chain and β-actin in skeletal muscle of female TIS21/BTG2/Pc3 knockout mice

Abstract

TIS21 belongs to antiproliferative gene family containing highly conserved BTG-Box A (Y50-N71) and Box B (L97-E115). Its orthologs in mouse, human and rat are TIS21, BTG2, Pc3, respectively. Based on our previous reports, mRNA expression of TIS21 is rather constitutive, but not inducible, in thymus, lung, kidney and basal cell layer of breast. We have previously reported potential roles of TIS21/BTG2 gene in mouse and human, e.g., the pan-cell cycle regulator in both G1/S and G2/M phase, a negative regulator of LSK (Lin-, Sca1+, c-Kit+) cell expansion in female mouse bone marrow, an inducer of cancer cell death under stressful condition such as serum starvation, cancer chemotherapy and hypoxia/reperfusion, a tumor suppressor in mouse thymus, lung and liver, and an inhibitor of cancer invasion in human bladder and breast tissues. In the present study, we explored whether TIS21 has any role in the regulation of metabolism, especially in skeletal muscle, in response to aging. Based on our cDNA analysis in the livers of TIS21-KO and wild type C57BL/6 mice, expression of muscle protein, e.g., α-actin and α-actinin, was significantly downregulated in the KO mice compared with those of the wild type after 20h fasting. Therefore, we examined expressions of skeletal muscle proteins such as myosin heavy chains, α-actinin and β-actin, along with degree of TIS21 expression in various muscle fibers by immunoblot analyses. From the trials, we could observe that expressions of myosin heavy chain and β-actin, but not α-actin and α-actinin, were significantly reduced in the gastrocnemius of TIS21-knockout female mice compared with those of the wild type. Moreover, the reduction of myosin heavy chain 1 was more severe when the TIS21-knockout mice were getting old. However, the phenomenon was not observed in male mice. Present data suggest a potential role of TIS21 gene in the metabolism of myosin heavy chain 1 and β-actin in skeletal muscle according to gender difference.

인간에서 골격근은 대략 전체 몸무게의 40%를 차지한다. 또한 골격의 근육은 기초대사량의 30%정도 차지한다고 알려져 있어 기초대사량을 결정하는 가장 중요한 인자이다. 그러나 노화나 대사 시스템에 문제가 발생하게 되면 근육이 퇴행함에 따라 근육에 저장된 단백질들이 아미노산으로 분해되어 근육양이나 근력이 감소되는 근감소증(Sarcopenia)이 발생한다. 본 연구에서 사용한 TIS21/BTG2/Pc3유전자는 항 증식 유전자 (Antiprolife rative gene)로 상동 범위인 Box-A (Tyr49-Asn71)와 Box-B (Leu96-Glu115)를 가진 세포성장억제 단백질 집단에 속한다. 본 연구의 목적은 TIS21/BTG2/Pc3이 노화에 따른 골격근 구조단백질 조절에서 어떠한 역할을 하는지를 밝혀내고자 TIS21/BTG2/Pc3 야생형과 유전자적중 마우스를 나이별, 성별로 희생하여 장딴지근 (Gastroc nemius)을 대상으로 다양한 근섬유들에서 TIS21/BTG2/Pc3 발현의 정도와 근섬유의 너비의 변화를 조절하는 골격근 구조 단백질 미오신중쇄와 세포 골격 베타액틴의 발현을 면역블롯팅(Immunoblotting) 통해 분석하였다. 그 결과 19개월 된 자성 TIS21 유전자적중 마우스에서 미오신중쇄 단백질과 베타액틴 단백질 양이 감소됨이 관찰 되었으며, 24개월 웅성에서는 이러한 현상이 관찰되지 않았다. 위 결과들로 미루어보아 TIS21/BTG2/Pc3 유전자는 노화에 따른 근육단백질 대사를 조절하는 것으로 예상된다.