STEM CELL FACTOR IS IMPLICATED IN MICROENVIRONMENTAL INTERACTIONS AND CELLULAR DYNAMICS OF CHRONIC LYMPHOCYTIC LEUKEMIA
Author(s): ,
George Gavriilidis
Affiliations:
Laboratory of Pharmacology, School of Pharmacy,Aristotle University of Thessaloniki,Thessaloniki,Greece
,
Stavroula Ntoufa
Affiliations:
Institute of Applied Biosciences,CERTH,Thessaloniki,Greece
,
Nikos Papakonstantinou
Affiliations:
Institute of Applied Biosciences,CERTH,Thessaloniki,Greece
,
Konstantia Kotta
Affiliations:
Institute of Applied Biosciences,CERTH,Thessaloniki,Greece
,
Elisavet Chartomatsidou
Affiliations:
Institute of Applied Biosciences,CERTH,Thessaloniki,Greece
,
Niki Stavroyianni
Affiliations:
Department of Hematology and HCT Unit,G. Papanicolaou Hospital,Thessaloniki,Greece
,
Achilles Anagnostopoulos
Affiliations:
Department of Hematology and HCT Unit,G. Papanicolaou Hospital,Thessaloniki,Greece
,
Eleni Papadaki
Affiliations:
Department of Medicine,University of Crete,Heraklion,Greece
,
Asterios S Tsiftsoglou
Affiliations:
Laboratory of Pharmacology, School of Pharmacy,Aristotle University of Thessaloniki,Thessaloniki,Greece
Kostas Stamatopoulos
Affiliations:
Institute of Applied Biosciences,CERTH,Thessaloniki,Greece
EHA Library. Gavriilidis G. Jun 15, 2019; 266747; PS1130
George Gavriilidis
George Gavriilidis
Contributions
Abstract

Abstract: PS1130

Type: Poster Presentation

Presentation during EHA24: On Saturday, June 15, 2019 from 17:30 - 19:00

Location: Poster area

Background

The mitogenic glycoprotein Stem Cell Factor (SCF, ligand of c-kit receptor) has been implicated as a pro-oncogenic driver in a variety of human cancers. Increased SCF levels have recently been reported in a small series of patients with chronic lymphocytic leukemia (CLL), however little if any evidence exists regarding its precise role in CLL pathophysiology.

Aims

To analyze the expression profile of SCF in a well-characterized cohort of CLL patients and investigate whether SCF is modulated by the CLL milieu.

Methods
CD19+ primary CLL cells were negatively selected. SCF transcripts were detected by qPCR, SCF protein levels were analyzed using Western Blotting (WB) and SCF+ cells were determined by Flow Cytometry (FC). Cellular proliferation (Ki-67+ cells) and oxidative stress (mitochondrial mass) were analyzed using FC. CLL cells were cultured in vitro with anti-IgM, CpG, CD40 ligand and H2O2, or co-cultured with the mesenchymal cell line HS-5. Secreted SCF was determined using ELISA in supernatants of CLL cells.

Results

Initially, we determined through qPCR (n=14) that CLL cells predominantly express the membrane-bound isoform of SCF, which is known to form a more stable complex with c-Kit, compared to the soluble isoform. Next, we found significantly increased SCF protein levels in CLL cells (n=68), compared to healthy tonsillar B cells (n=13) (FD:9.8; p<0.001). Within our CLL cohort, increased SCF protein levels significantly correlated with CD38 positivity (FD:2.45; p<0.05), ZAP70 positivity (FD: 2; p<0.05), trisomy 12 (FD:3; p<0.05), and a shorter time to first treatment (p<0.01). Moreover, increased SCF protein levels and SCF+ cells strongly correlated with the expression of unmutated IGHV genes (FD:6.7; p<0.001 and FD:4.8; p<0.01 respectively).

Next, we investigated whether stimulants mimicking the CLL milieu in vitro could modulate SCF protein expression in CLL cells. Stimulation of the B cell receptor (BCR) significantly increased SCF protein levels (n=11, FD:1.4; p<0.001). TLR-9 stimulation significantly increased SCF+ cells (n=8, FD:1.5; p<0.01) and induced the secretion of soluble SCF (n=7, FD:9.3; p<0.05). Co-stimulation of TLR9/CD40 receptors induced Ki-67+ (FD:7.1; p<0.01) and SCF+ (FD:3.8; p<0.01) cells. Of note, 85% of the proliferating CLL cells were also SCF+ (Ki-67+/SCF+ vs Ki-67+/SCF-; p<0.01). The in vitro modulation of SCF in CLL cells by immune determinants prompted us to investigate whether B cell signaling inhibition might also modulate SCF expression in vivo. Longitudinal profiling of 6 CLL patients under Ibrutinib therapy showed a significant decrease in SCF+ cells at +1 month under treatment, compared to the pre-treatment samples (FD:2.2; p<0.05), further highlighting the links between immune signaling and SCF expression in CLL.

Finally, co-culturing of CLL cells (n=12) with the HS-5 cells significantly reduced SCF+ cells (FD:2.2; p<0.001), in parallel with a decrease in mitochondrial mass (r=0.73; p<0.01). Treatment with H2O2 abrogated the anti-oxidant protection of HS-5 cells and up-regulated SCF expression (FD=1.9; p<0.01), indicating that SCF expression in CLL cells is modulated by oxidative stress.

Conclusion

Overexpression of membrane-bound SCF in CLL is associated with adverse prognosis and a shorter time-to-first treatment. Microenvironmental cues modulate the expression and secretion of SCF isoforms by CLL cells, highlighting a crucial role for this inflammatory growth factor in CLL cell homeostasis.

Session topic: 5. Chronic lymphocytic leukemia and related disorders - Biology & Translational Research

By continuing to browse or by clicking “Accept Terms & all Cookies”, you agree to the storing of third-party cookies on your device to enhance your user experience and agree to the user terms and conditions of this learning management system (LMS).

Cookie Settings
Accept Terms & all Cookies