Proteomic analysis of media from lung cancer cells reveals role of 14-3-3 proteins in cachexia

Abstract

Aims: At the time of diagnosis, 60% of lung cancer patients present with cachexia, a severe wasting syndrome that increases morbidity and mortality. Tumors secrete multiple factors that contribute to cachectic muscle wasting, and not all of these factors have been identified. We used Orbitrap electrospray ionization mass spectrometry to identify novel cachexia-inducing candidates in media conditioned with Lewis lung carcinoma cells (LCM). Results: One-hundred and 58 proteins were confirmed in three biological replicates. Thirty-three were identified as secreted proteins, including 14-3-3 proteins, which are highly conserved adaptor proteins known to have over 200 binding partners. We confirmed the presence of extracellular 14-3-3 proteins in LCM via western blot and discovered that LCM contained less 14-3-3 content than media conditioned with C2C12 myotubes. Using a neutralizing antibody, we depleted extracellular 14-3-3 proteins in myotube culture medium, which resulted in diminished myosin content. We identified the proposed receptor for 14-3-3 proteins, CD13, in differentiated C2C12 myotubes and found that inhibiting CD13 via Bestatin also resulted in diminished myosin content. Conclusions: Our novel findings show that extracellular 14-3-3 proteins may act as previously unidentified myokines and may signal via CD13 to help maintain muscle mass.

Cancer and Chemotherapy Contribute to Muscle Loss by Activating Common Signaling Pathways

“…Furthermore, proteins of the 14-3-3 family were also shown to be decreased both in tumor hosts and Folfiri-treated animals. Interestingly, these proteins were recently identified as novel myokines required for maintaining myosin content in skeletal muscle (McLean et al, 2015 ).…”

Cancer cachexia—when proteasomal inhibition is not enough

“…should encourage us to look into proteasome‐ and NF‐kB‐independent signalling pathways involved in cancer cachexia and identify novel targets to treat this syndrome. Further studies are needed to elucidate precise signalling pathways involved in cancer cachexia; and first steps towards this direction are already being taken . Some of the factors increased in cancer cachexia, such as angiotensin II, and the transforming growth factor beta family members myostatin and activin A, have already been identified.…”

“…If myostatin inhibitors are beneficial as therapies for cancer, associated muscle wasting is currently being tested in clinical trials. Further mechanisms, which are involved in the pathogenesis of cancer cachexia include growth differentiation factor‐15, macrophage inhibitory cytokine‐1, leukaemia inhibitory factor, Fn14, signal transducer and activator of transcription 3, parathyroid hormone‐related protein, and histone deacetylases; and this list is steadily increasing . Future studies need to be performed in a tumour‐specific and disease stage‐dependent manner to answer the question why certain cancers are more prone to cause cachexia than others, and to identify tumour‐specific differences in cachexia pathways.…”

“…Further studies are needed to elucidate precise signalling pathways involved in cancer cachexia; and first steps towards this direction are already being taken. 92,93 Some of the factors increased in cancer cachexia, such as angiotensin II, 94 and the transforming growth factor beta family members myostatin 95 and activin A, 96 have already been identified. Especially, myostatin and activin A are up-regulated in patients with various types of malignancies (for a review, see 97 ).…”

“…Further mechanisms, which are involved in the pathogenesis of cancer cachexia include growth differentiation factor-15, macrophage inhibitory cytokine-1, 101,102 leukaemia inhibitory factor, 103 Fn14, 104 signal transducer and activator of transcription 3, 105 parathyroid hormone-related protein, 106 and histone deacetylases; 107 and this list is steadily increasing. 92,93 Future studies need to be performed in a tumour-specific and disease stage-dependent manner to answer the question why certain cancers are more prone to cause cachexia than others, and to identify tumour-specific differences in cachexia pathways. Information gained by those studies will be useful to develop target and disease stage-specific treatments.…”