Constitutive activation of STAT3 in Sézary syndrome is independent of SHP-1

Abstract

Constitutive and persistent activation of STAT3 has been implicated in the pathogenesis of many malignancies. Studies of CTCL cell lines have previously suggested that aberrant activation of STAT3 is mediated via silencing of the negative regulator SHP-1 by promoter methylation. In this study of ex vivo tumour cell populations from 18 Sé zary syndrome (SS) patients, constitutive phosphorylation of STAT3, JAK1 and JAK2 was present in all patients, but was absent in comparative CD4 þ T-cells from healthy controls. Furthermore, no loss or significant difference in SHP-1 expression was observed between patients and healthy control samples. Methylationspecific PCR analysis of the SHP-1 CpG island in 47 SS patients and 11 healthy controls did not detect any evidence of methylation. Moreover, small interfering RNA knockdown of SHP-1 had no effect on phosphorylation of STAT3. In contrast, treatment of SS tumour cells with the pan-JAK inhibitor pyridone 6 led to downregulation of phosphorylated STAT3 (pSTAT3), its target genes and induction of apoptosis. No evidence for common JAK1/JAK2-activating mutations was found. These data demonstrate that constitutive activation of STAT3 in SS is not due to the loss of SHP-1, but is mediated by constitutive aberrant activation of JAK family members.

Romidepsin in peripheral and cutaneous T‐cell lymphoma: mechanistic implications from clinical and correlative data

“…HDAC inhibitors increase global histone acetylation in cancer cells and promote T-cell apoptosis (Zhang et al, 2005;Shao et al, 2010). While studies have begun to identify the molecular basis of the various subtypes of mature T-cell lymphomas (Campbell et al, 2010;Lemonnier et al, 2012;McKenzie et al, 2012;Ferrara et al, 2013;Palomero et al, 2014), responses to romidepsin and belinostat have been reported across the entire disease spectrum, without regard to subtype. The precise mechanism underlying activity against T-cell lymphoma has yet to be determined, and multiple biological effects have been invoked.…”

Cutaneous Lymphomas: Molecular Pathways Leading to New Drugs

“…Phosphorylation of JAK1 and JAK2, but not activating mutations in these two enzymes, also contributes to the constitutive STAT3 activation, which is independent of downregulation or loss of SHP-1 tyrosine phosphatase. In this respect, the use of JAK inhibitors represents a promising therapeutic option already confirmed by in vitro data (McKenzie et al, 2011).…”

Contribution of STAT3 and RAD23B in Primary Sézary Cells to Histone Deacetylase Inhibitor FK228 Resistance

“…HUT-78 cells were electroporated using the Gene Pulser® II Electroporation System (Biorad) at 240V and 975uF with 100 nM of RAD23B-specific (D-011759-04) or scrambled siRNA (D-001206-13-05; both Dharmacon) and cultured for 48 hours as described (Verma et al 2010) . RAD23B depletion was confirmed by immunoblot and by PCR of cDNA using RAD23B-specific primers (5'-TGACCCCGAGGAGACGGTGA-'3; reverse: 5'-GCAGGTGTGGAAGTGGGGGC-'3) and cyclophilin-specific primers as described (McKenzie et al 2012).…”