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Stable alterations of CD44 isoform expression in prostate cancer cells decrease invasion and growth and alter ligand
Kui Yang1, Yaqiong Tang, Gabriel K Habermehl
1Department of Pathology, University of Colorado Denver Health Science Center, Aurora, Colorado, USA.
Background:
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 isoform, CD44v7-10.
Methods:
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. Expression responses of merlin, a CD44 binding partner, and growth-permissive phospho-merlin, were assessed by western blot.
Results:
Compared to luciferase-only PC-3M cells, all three 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 two CD44s re-expression approaches caused minimal sensitization. In limited numbers of mouse subcutaneous xenografts, all three alterations produced only nonsignificant trends toward slower growth compared with luciferase-only controls. The expression of CD44s as a separate protein, but not a fusion protein, caused emergence of a strongly-expressed, hypophosphorylated species of phospho-merlin.
Conclusion:
Stable re-expression of CD44s reduces PCa growth and invasion in vitro, and possibly in vivo, suggesting CD44 alterations have potential as gene therapy. When the C-terminus of CD44s is fused to another protein, most phenotypic effects are lessened, particularly hyaluronan adhesion. Finally, CD44v7-10, although it was not functionally significant for growth, may be a target for chemosensitization.
Insights
Re-expressing CD44 standard (CD44s) in prostate cancer (PCa) cells reduced tumor growth and invasion. CD44v7-10 may be a target for improving chemotherapy sensitivity in PCa.
Area of Science:
- Oncology
- Molecular Biology
- Cancer Genetics
Background:
- Dysregulated CD44 expression is common in human cancers, including prostate cancer (PCa).
- Prostate cancer (PCa) exhibits reduced CD44 standard (CD44s) and increased CD44 variant 7-10 (CD44v7-10) expression.
- CD44 is a cell surface glycoprotein involved in cell adhesion, migration, and proliferation.
Purpose of the Study:
- To investigate the functional impact of CD44 standard (CD44s) re-expression and CD44 variant 7-10 (CD44v7-10) knockdown in prostate cancer (PCa) cells.
- To evaluate the effects on cancer cell invasion, migration, proliferation, adhesion, and chemosensitivity.
- To assess the potential of CD44 alterations as a gene therapy strategy for PCa.
Main Methods:
- Utilized retroviral gene delivery to express CD44s (as a fusion or separate protein) or knock down CD44v7-10 in PC-3M PCa cells.
- Assessed invasion, migration, proliferation, soft agar colony formation, adhesion, and Docetaxel sensitivity.
- Analyzed xenograft growth and expression of merlin and phospho-merlin via western blot.
Main Results:
- Re-expression of CD44s, either as a separate or fusion protein, reduced invasion and migration.
- CD44s re-expression significantly enhanced hyaluronan and osteopontin binding, particularly as a separate protein.
- CD44v7-10 knockdown sensitized PCa cells to Docetaxel, while CD44s re-expression had minimal effect.
- CD44s re-expression as a separate protein led to the emergence of hypophosphorylated phospho-merlin.
Conclusions:
- Stable CD44s re-expression inhibits PCa growth and invasion in vitro, showing potential for gene therapy.
- Fusion of CD44s to other proteins diminishes its phenotypic effects, especially hyaluronan adhesion.
- CD44v7-10 may serve as a therapeutic target for enhancing chemosensitization in prostate cancer (PCa).
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