Abstract LB-103: Signaling via CD44v6 is associated with the growth of CD44-expressing glioma stem-like cells
Authors: Jijiwa Mayumi , Gupta Snehalata , Demir Habibe , Leung Crystal , Chaudhury Abhik Ray , Kornblum Harley I. , Nakano Ichiro 
Published: June 2012

Background: Brain tumors contain stem-like cells are likely a therapeutic target in malignant glioma due to their therapeutic resistance and ability of tumor initiation. Several studies have suggested the presence of multiple types of brain tumor stem-like cells (BTSC). However, the molecular markers valuable for targeting these subpopulations of glioma cells are still unknown. CD44 is a cell surface protein linked to tumorigenesis in some cancers outside of the central nervous system (CNS). CD44 expression is recognized in various types of cancer stem cells. In particular, one of CD44 variant isoforms, CD44v6, is associated with malignant transformation of non-CNS tumor cells by inducing proliferation and migration. To date, expression and function of CD44 and CD44v6 in BTSC is not characterized yet. Here, we investigated the expression of CD44, including CD44v6, and their function in BTSC.

Results: RT-PCR and Western blotting elucidated that a subset of GBM expresses high level of CD44. Immunostaining on glioma tissue microarray demonstrated that patients with high grade glioma expressing CD44 had poorer prognoses. Positive staining of CD44 on tumor cell surface was seen only in glioblastoma multiforme (GBM). FACS analysis of BTSC enriched from GBM specimens showed a subset of GBM expressed high level of CD44 in BTSC. CD44 neutralizing antibody inhibited cell growth of BTSC derived from CD44-high GBM, while BTSC from CD44-low GBM was not affected. Cultured BTSC from CD44-high GBM contains subpopulation expressing CD44v6. Knockdown of CD44v6 with siRNA inhibited in vitro growth of BTSC from CD44-high GBM but not from CD44-low GBM. This inhibition did not affect growth of cells derived from the same tumors that do not have stem-like characters. CD44 ligand osteopontin (OPN) activated AKT in BTSC from CD44-high GBM, but not in CD44-low samples. With CD44v6 knockdown, both phosphorylated AKT and S6R were under detectable level and OPN failed to activate AKT and S6R, while EGF substantially increased both molecules. When the PI3K/AKT pathway was inhibited by five different small molecules, a dose-dependent inhibition for neurosphere formation was observed for all inhibitors in BTSC from CD44-high GBM. In contrast, BTSC from CD44-low GBM were relatively resistant to the treatment.

Conclusion: Our data indicate that a subset of GBM expresses high level of CD44 and CD44v6 in BTSC. GBM expressing high level of CD44 depends on CD44v6 on the growth of their BTSC. This action of CD44v6 is, at least in part, mediated through the AKT pathway. CD44 expression in high grade glioma corresponds to poorer prognosis. Immunoreactive site of CD44 on GBM cells correlates with pathological grade.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr LB-103. doi:10.1158/1538-7445.AM2011-LB-103