Altered expression of skeletal muscle myosin isoforms in cancer cachexia

Cachexia is commonly seen in cancer and ischaracterized by severe muscle wasting, but little is known about theeffect of cancer cachexia on expression of contractile protein isoforms such as myosin. Other causes of muscle atrophy shift expression ofmyosin isoforms toward increased fast (type II) isoform expression. Weinjected mice with murine C-26 adenocarcinoma cells, a tumor cell linethat has been shown to cause muscle wasting. Mice were killed 21 daysafter tumor injection, and hindlimb muscles were removed. Myosin heavychain (MHC) and myosin light chain (MLC) content was determined inmuscle homogenates by SDS-PAGE. Body weight was significantly lower intumor-bearing (T) mice. There was a significant decrease in muscle massin all three muscles tested compared with control, with the largestdecrease occurring in the soleus. Although no type IIb MHC was detectedin the soleus samples from control mice, type IIb comprised 19% of thetotal MHC in T soleus. Type I MHC was significantly decreased in T vs. control soleus muscle. MHC isoform content was not significantly different from control in plantaris and gastrocnemius muscles. Thesedata are the first to show a change in myosin isoform expression accompanying muscle atrophy during cancer cachexia.