and mRNA levels were quantified by realtime quantitative polymerase chain reaction (RQ-PCR) (for more details please see the and gene splice variants in CLL cells by RQ-PCR analysis. of immune receptors and long-term cell-cell interactions with the mesenchymal stroma led to an elevation of SCF primarily in CLL cases with an adverse prognosis. Contrariwise, suppression of oxidative stress and the BYK 204165 BTK inhibitor ibrutinib lowered SCF levels. Interestingly, SCF significantly correlated with mitochondrial dynamics and hypoxia-inducible factor-1a which have previously been linked with clinical aggressiveness in CLL. SCF was able to elicit direct biological effects in CLL cells, affecting redox homeostasis and cell proliferation. Overall, the aberrantly expressed SCF in CLL cells emerges as a key response regulator to microenvironmental stimuli while correlating with poor prognosis. On these grounds, specific targeting of this inflammatory molecule could serve as a novel therapeutic approach in CLL Introduction Chronic inflammation facilitates the survival, proliferation and immune evasion of chronic lymphocytic leukemia (CLL) cells in their tissue microenvironments.1,2 CLL cells aberrantly express pro-inflammatory mediators such as cytokines and chemokines due to intrinsic abnormalities (e.g., mutations in or other genes) or extrinsic determinants (e.g., antigenic stimulation of B-cell receptors [BcR] and Toll-like receptors [TLR]).1,3 Moreover, CLL cells further exacerbate the inflammatory character of their respective tumor milieu by modulating their surrounding cells in a pro-oncogenic fashion.4 Inflammation in the CLL milieu is linked with the clinical heterogeneity of the disease since BYK 204165 increased levels of cytokines/chemokines correlate with adverse prognostic markers such as high ZAP70 and CD38 expression, unmutated IGHV genes, aggressive stereotyped subsets (e.g., subset #1) and adverse prognostic chromosomal aberrations such as del(11q) and del(17p).5C7 Gradually, inflammation favors the expansion of more aggressive CLL clones that ultimately lead to chemorefractoriness.1,7 Hence, deciphering the complex biology of inflammation in the CLL microenvironment is paramount for the successful “bench-to-bedside” transition of novel therapeutics that will drastically improve the outcomes of CLL patients. Recently, the mitogenic BYK 204165 cytokine stem cell factor (SCF, KIT ligand, encoded by the gene) was found to be increased in the serum of CLL patients and also expressed by CLL cells infiltrating the bone marrow and lymph nodes.7-9 SCF is a pro-inflammatory glycoprotein that, upon homo-dimerization, binds to the c-kit receptor (gene, CD117), a class III receptor tyrosine kinase that is primarily localized around the cell surface but can also be found in the cytoplasm and the nucleus.10-12 There are two major option splice variants of the gene, distinguished based on the presence or not of a specific exon (exon 6) that encodes a proteolytic cleavage site. The variant of the gene carrying exon 6 encodes a transiently transmembrane isoform that is swiftly released after proteolytic cleavage from BYK 204165 metalloproteases such as MMP-9 (soluble SCF, KL-1). The variant lacking exon 6 encodes a predominantly transmembrane isoform that can also be processed by metalloproteases albeit with less affinity (membrane SCF, KL-2). The KL-2 isoform elicits a more durable activation of c-kit whereas the KL-1 isoform elicits a more rapid but transient activation due to ensuing receptor internalization.13,14 Both isoforms induce cell proliferation and differentiation albeit with distinct efficacy depending on the tissue involved, the available synergistic growth factors and the developmental stage of the c-kit+ cells.12,15 Furthermore, the KL-1 isoform serves as a chemoattractant whereas the KL-2 isoform is involved in cellular adhesion.16,17 Both SCF isoforms increase in inflamed tissues due to reactive oxygen species (ROS) and potentiate the alleviation of excessive oxidative stress, thus functioning as compensatory survival factors.18,19 SCF is considered an adverse prognostic marker in cancer, correlating with shorter overall and relapse-free survival as well as increased angiogenesis.20 Furthermore, activation of c-kit by BYK 204165 SCF binding promotes survival, proliferation, stemness, immune evasion and drug resistance of malignant cells while it potentiates their metastatic dissemination. 15,21-23 SCF overproduction by cancer cells leads to a plethora of interactions with surrounding c-kit+ cells which underpins the prevalence of the tumor microenvironment at the expense of the neighboring normal cellular Mouse Monoclonal to Rabbit IgG niches.24 There is scant information regarding the role of SCF in the pathobiology of.