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Am J Translational Res 2011;3(1):1-7

Review Article
Cell adhesion molecule CD44: its functional roles in prostate cancer

Kenneth A. Iczkowski

Department of Pathology, University of Colorado Health Science Center, Aurora, CO 80045, USA.

Received: August 17, 2010; accepted: August 29, 2010; Epub: September 12, 2010; Published: January 1, 2011

Abstract: CD44 is a cell adhesion glycoprotein that also governs cell signaling.  Dysregulated CD44 expression
characterizes most human cancers, including prostate cancer (PCa). PCa loses expression of CD44 standard
(CD44s) that is present in benign epithelium, and overexpresses the novel splice variant (v) isoform, CD44v7-10.  
We studied CD44 in PCa for more than a decade, and in a series of papers, established its functional
significance.  Using retroviral gene delivery to PC-3M PCa cells, we expressed luciferase-only, enforced CD44s
re-expression as a fusion protein with luciferase at its C-terminus or as a protein separate from luciferase, or
knocked down CD44v7-10 by RNAi. Invasion, migration, proliferation, soft agar colony formation, adhesion,
Docetaxel sensitivity, and xenograft growth assays were carried out. Compared to luciferase-only PC-3M cells, all
3 treatments reduced invasion and migration. Growth and soft agar colony formation were reduced only by
re-expression of CD44s as a separate or fusion protein but not CD44v7-10 RNAi. Hyaluronan and osteopontin
binding were greatly strengthened by CD44s expression as a separate protein, but not a fusion protein.
CD44v7-10 RNAi in PC-3M cells caused marked sensitization to Docetaxel; the 2 CD44s re-expression
approaches caused minimal sensitization. In limited numbers of mouse subcutaneous xenografts, all 3
alterations produced only nonsignificant trends toward slower growth compared with luciferase-only controls. In
further work, we tested the effects of the anti-growth compound silibinin, a milk thistle derivative.  Using a
luciferase promoter construct to test for CD44 promoter activity, silibinin significantly and dose-dependently
inhibited promoter activity at physiologic doses. Total CD44 RNA and CD44v7-10 RNA were significantly
decreased; both were also decreased at the protein level. Phenyl-methylene hydantoins (PMH), guanidine
alkaloids derived from Red Sea sponges, have the ability to increase cell-cell adhesion in prostate cancer cells
and reduce invasion. Expression of CD44 total mRNA and CD44v7-10 were markedly decreased by PMH and its
S-ethyl derivative.  The oncogenic microRNAs, miR-373 and miR-520c, which interact with CD44, were studied in
prostate cancer cells and human tissues. We found that they bound the 3' untranslated region of the CD44 RNA,
and suppressed CD44 in prostate cancer, by preventing the translation of CD44 RNA, rather than by degrading
the RNA.  Thus, stable re-expression of CD44s reduces PCa growth and invasion in vitro, and possibly in vivo,
suggesting CD44 potential as gene therapy. Finally, CD44v7-10 may be a target for chemosensitization, and
plays a role in nutraceutical abrogation of tumor development. In vivo effects of CD44 alteration still need to be
investigated by use of orthotopic or renal capsule xenografts, which confer a different stromal microenvironment
than that of the subcutaneous grafts.  (AJTR1008003).

Key words: CD44, prostate, splicing, standard, variant, silibinin, phenyl-methylene hydantoins, xenografts

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Address all correspondence to:
Kenneth A. Iczkowski, MD
Department of Pathology
University of Colorado Health Science Center
Aurora, CO 80045, USA
Tel: 303-724-0155, Fax: 303-724-3712