YAP Involves in Reduced Anabolic Response to Functional Overload in Lewis Lung Carcinoma‐bearing Mice

Abstract

Cancer‐associated weight loss, also known as cachexia, is connected to poor prognosis, reduced response to chemotherapy, and impaired patient quality of life. While resistance exercise/muscle contraction is a promising therapy, anabolic resistance, the suppressed ability to induce protein synthesis, is present and can’t be solely elucidated by the change of mTOR signaling. Yes‐associated protein (YAP) is a downstream effector of Hippo signaling and is known to control skeletal muscle size in response to mechanical stimulus. However, the role of YAP on anabolic resistance in cancer cachexia needs to be clarified. The purpose of this study was to determine whether the state of YAP activity after functional overload is altered in cachectic mice. Approximately three‐month‐old male C57BL6 mice were divided into two groups: Control group with PBS (100 μl) injection (Con, n=5) and tumor‐implantation group with Lewis lung Carcinoma (LLC) cells injection (2×105 cells in 100 μl PBS, LLC, n=5). Injection was made at the right flank under anesthesia. Four weeks after injection tumor growth was visible, synergist ablation surgery was performed on the left leg (Overload) and the right leg served as an internal control with sham surgery (Sham). Puromycin (0.04 μmol/g body weight, BW) was injected 30 minutes prior to sacrifice and plantaris muscles (PLAN) were removed and snap‐frozen at day 7 following the surgery. After total protein was extracted, routine Western blotting was performed using 60~120 μg of the total protein. Paired t‐test (Sham vs. Overload) and unpaired t‐test (Con vs. LLC) were used for statistical analysis and the levels of significance was set at 0.05. PLAN weights were comparable between Con and LLC with sham surgery (19.8±1.2 mg vs. 17.3±0.5 mg for Con and LLC, respectively, p=0.077). Seven‐day functional overload increased PLAN weights regardless of tumor inoculation, but the degree of hypertrophy was different (42.7±4.0% vs. 27.6±4.6% for Con and LLC, respectively, p<0.05). LLC mice showed reduced levels of phosphorylated p70S6K (p‐p70) with sham surgery (1.0±0.3 vs. 0.4±0.1, for Con and LLC, respectively, p<0.05) and those with SA surgery (4.4±0.7 vs. 1.6±0.7, for Con and LLC, p<0.05). In harmony with these results, the basal levels of muscle protein synthesis in LLC mice were decreased by 51% compared to Con mice and the levels remained lower after functional overload (2.1±0.1 vs. 1.1±0.1 for Con and LLC, respectively, p<0.05). Interestingly, the basal phosphorylated levels of YAP (p‐YAP) were elevated in LLC mice (1.0±0.1 vs. 2.2±0.1, for Con and LLC, respectively, p<0.05). However, functional overload did not alter the levels of p‐YAP in LLC mice while Con mice significantly increased the levels by 55% (p<0.05). In conclusion, the data suggest that YAP plays a role, at least in part, in decreased anabolic response to functional overload in LLC‐bearing mice.Support or Funding InformationSupported by Louisiana Board of Regents Support Fund (LEQSF(2017‐20)‐RD‐A‐22) to SS.