Expression of Activated STAT5 in Neoplastic Mast Cells in Systemic Mastocytosis

Abstract

Recent data suggest that the signal transducer and activator of transcription (STAT)5 contributes to differentiation and growth of mast cells. It has also been described that constitutively phosphorylated STAT5 (pSTAT5) plays a pro-oncogenic role in various myeloid neoplasms. We examined the expression of pSTAT5 in neoplastic mast cells in systemic mastocytosis and asked whether the disease-related oncoprotein KIT D816V is involved in STAT5 activation. As assessed by immunohistochemistry using the anti-pSTAT5 antibody AX1, neoplastic mast cells were found to display pSTAT5 in all SM patients examined (n = 40). Expression of pSTAT5 was also demonstrable in the KIT D816V-positive mast cell leukemia cell line HMC-1. Using various staining-protocols, pSTAT5 was found to be located in both the cytoplasmic and nuclear compartment of mast cells. To define the functional role of KIT D816V in STAT5-activation, Ba/F3 cells with doxycycline-inducible expression of KIT D816V were used. In these cells, induction of KIT D816V resulted in an increased expression of pSTAT5 without substantial increase in total STAT5. Moreover, the KIT D816V-targeting kinase-inhibitor PKC412 was found to counteract expression of pSTAT5 in HMC-1 cells as well as doxycycline-induced expression of pSTAT5 in Ba/F3 cells. Finally, a dominant negative STAT5-construct was found to inhibit growth of HMC-1 cells. Together, our data show that neoplastic mast cells express cytoplasmic and nuclear pSTAT5, that KIT D816V promotes STAT5-activation, and that STAT5-activation contributes to growth of neoplastic mast cells.

Oncogenic KIT mutations in different exons lead to specific changes in melanocyte phospho-proteome

“…Previous studies showed that in neoplastic mast cells and in leukemia KIT D816H mutations lead to STAT3 and STAT5 activation [29–31]. We found similar changes in STAT signaling using melanocytes strongly suggesting a distinct effect of the KIT mutation rather than a cell specific change.…”

Regulation of Stat5 by FAK and PAK1 in Oncogenic FLT3- and KIT-Driven Leukemogenesis

“…Active Stat5 is thought to play an essential role in regulating the transformation of FLT3 and KIT oncogene bearing cells (Baumgartner et al, 2009; Brady et al, 2012). Although Stat5 is a transcription factor, mechanism(s) involved in the transport of this molecule in and out of the nucleus in oncogene bearing cells remains poorly understood.…”

“…Presence of phosphorylated (p) pStat5 in newly diagnosed AML patients is also associated with poor overall survival (Brady et al, 2012). Constitutive activation of pStat5 is observed in 100% of systemic mastocytosis (SM) patients bearing the KITD816V mutation (Baumgartner et al, 2009). A strong correlation between the presence of pStat5 and FLT3ITD mutations is seen in AML patients and FLT3ITD expression results in constitutive Stat5 phosphorylation (Obermann et al, 2010) (Spiekermann et al, 2003), (Choudhary et al, 2007; Choudhary et al, 2005).…”

Mast cell homeostasis and the JAK–STAT pathway

“…95 Clinically, neoplastic mast cells in SM patients have been shown to unanimously express elevated levels of phosphorylated STAT5 found in both the cytoplasm and the nucleus of mast cells, an effect that was attributed to D816V c-kit signaling and blunted by inhibition of D816V kinase activity. 101 …”