Butyrate Alters mRNA and Protein Levels of Tumorigenic Chemokines in U937 Leukemic Cells

Abstract

Butyrate (NaB) is a HDAC inhibitor implicated as a potential therapy for cancer. Due to its ability to promote gamma globin, low concentrations (<1.5 mM) are used for treatment of hemoglobin disorders. Conversely, high concentrations (>1.5 mM) activate apoptosis in several cancer cell lines. Low concentrations of NaB influence signaling pathways that modulate cytokine production. However, it is not known whether high concentrations alter these pathways thereby regulating cytokine expression in cancer cells and altering the microenvironment, which was the purpose of this study. We exposed leukemia cells to high concentrations of NaB and analyzed for apoptosis, cytokine mRNA and protein levels, and chemotaxis. Our results show NaB induced activation of caspase‐3, but significantly decreased chemokine CCL2 and CCL5 mRNA and protein levels. Moreover, monocyte migration towards culture media from NaB‐treated cells significantly decreased. To elucidate the signaling mechanism, we investigated if NaB alters activation of AKT, MAPK, and Jak proteins. NaB induced p38, but suppressed ERK and AKT. NaB did not influence JNK or Jak proteins. Pretreatment with a p38 inhibitor abolished NaB‐induced reduction in CCL5; however, this was not observed in CCL2. This data suggests that while promoting apoptosis, NaB influences the cancer microenvironment by decreasing chemokine production via the MAPK pathway. These effects may influence the biology of normal and cancer cells thereby altering the status of the patient receiving NaB therapy. Ms Pulliam is supported by NHLBI T32 Pre‐doctoral training grant 2 T32 HL007735‐16 to Dr. Adunyah and CTSA award UL1TR000445 from the NCATS. Dr. Adunyah is supported by NCI U54 grant 5 U54 CA163069‐02 and NIMHD MeTRC grant 8 U54 MD007593‐04.