He selection of the distal 3′ splice site, resulting in VEGFb production

He selection of the distal 3′ splice site, resulting in VEGFb production126. These results suggest that signaling-mediated VEGF alternative splicing controls the balance of pro-angiogenic VEGF and anti-angiogenic VEGFb. This view was further supported by a recent finding showing that mutations in WT1, the Wilm’s tumor suppressor gene, suppress the production of VEGF165b, causing abnormal activity of angiogenesis and PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19851335 Wilms’ tumors128. WT1 represses the transcription of SRPK1 by directly binding to its promoter. SRPK1 phosphorylates SRSF1 that enhances the ability of SRSF1 to promote the production of VEGF. Thus, in WT1 mutant cells SRPK1 is highly expressed, resulting in hyperphosphorylation of SRSF1, which in turn favors the production of VEGF and renders the WT1 mutant cells proangiogenic128. Currently, the available anti-VEGF IMR 1 cancer therapeutics, such as the anti-VEGF antibody Peretinoin web Bevacizumab, does not distinguish between different spliced isoforms of VEGF129. This poses a dilemma in clinics as VEGF165b competes with VEGF165 for binding to Bevacizumab, resulting in drug resistance and side effects129. Therefore, understanding the Author Manuscript Author Manuscript Author Manuscript Author Manuscript Wiley Interdiscip Rev RNA. Author manuscript; available in PMC 2015 May 10. Liu and Cheng Page 7 mechanisms to manipulate the production of VEGFb may lead to a novel therapeutic strategy for reduction of tumor angiogenesis. Activating invasion and metastasis As tumors progress to higher pathological grades of malignancy, cancer cells typically begin to develop alterations in cell shapes and the ability to attach to other cells and to extracellular matrix. These series of discrete changes prepare cancer cells for local invasion and distal metastasis130. Recent studies have shown that a developmental process epithelial-mesenchymal transition is hijacked by cancer cells to disseminate to distant organs131134. When EMT occurs, the tightly packed epithelial cells become loosely connected and transit to spindle-shaped mesenchymal cells that show high degree of migratory ability. It was recently shown that alternative splicing represents a novel mechanism that causally controls EMT135. Work from our group has demonstrated that alternative splicing of the CD44 gene is dynamically regulated during EMT135. In epithelial cells, the variable exon-containing CD44v is predominant. When cells undergo EMT, there is a gradual loss of CD44v and gain of the short CD44s isoform, resulting in a nearly complete switch in expression to CD44s in mesenchymal cells. Importantly, this CD44 isoform switching is required for cells to undergo EMT and for the formation of breast tumors that display EMT characteristics in mice. Analysis of breast cancer patient specimens showed that CD44s is up-regulated in high-grade breast tumor tissues and positively correlates with the mesenchymal status of these tumors135. This study demonstrated that cells utilize alternative splicing as a means to regulate EMT by producing a specific CD44 isoform that acts as a key mediator of EMT. Studies on the role of CD44s revealed that CD44s potentiates Akt signaling and promotes cell survival153, an activity that differs from the proliferative advantage mediated by CD44v shown in Author Manuscript Author Manuscript Author Manuscript Author Manuscript Wiley Interdiscip Rev RNA. Author manuscript; available in PMC 2015 May 10. Liu and Cheng Page 8 presence of oxygen, leading to a state that has b.He selection of the distal 3′ splice site, resulting in VEGFb production126. These results suggest that signaling-mediated VEGF alternative splicing controls the balance of pro-angiogenic VEGF and anti-angiogenic VEGFb. This view was further supported by a recent finding showing that mutations in WT1, the Wilm’s tumor suppressor gene, suppress the production of VEGF165b, causing abnormal activity of angiogenesis and PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19851335 Wilms’ tumors128. WT1 represses the transcription of SRPK1 by directly binding to its promoter. SRPK1 phosphorylates SRSF1 that enhances the ability of SRSF1 to promote the production of VEGF. Thus, in WT1 mutant cells SRPK1 is highly expressed, resulting in hyperphosphorylation of SRSF1, which in turn favors the production of VEGF and renders the WT1 mutant cells proangiogenic128. Currently, the available anti-VEGF cancer therapeutics, such as the anti-VEGF antibody Bevacizumab, does not distinguish between different spliced isoforms of VEGF129. This poses a dilemma in clinics as VEGF165b competes with VEGF165 for binding to Bevacizumab, resulting in drug resistance and side effects129. Therefore, understanding the Author Manuscript Author Manuscript Author Manuscript Author Manuscript Wiley Interdiscip Rev RNA. Author manuscript; available in PMC 2015 May 10. Liu and Cheng Page 7 mechanisms to manipulate the production of VEGFb may lead to a novel therapeutic strategy for reduction of tumor angiogenesis. Activating invasion and metastasis As tumors progress to higher pathological grades of malignancy, cancer cells typically begin to develop alterations in cell shapes and the ability to attach to other cells and to extracellular matrix. These series of discrete changes prepare cancer cells for local invasion and distal metastasis130. Recent studies have shown that a developmental process epithelial-mesenchymal transition is hijacked by cancer cells to disseminate to distant organs131134. When EMT occurs, the tightly packed epithelial cells become loosely connected and transit to spindle-shaped mesenchymal cells that show high degree of migratory ability. It was recently shown that alternative splicing represents a novel mechanism that causally controls EMT135. Work from our group has demonstrated that alternative splicing of the CD44 gene is dynamically regulated during EMT135. In epithelial cells, the variable exon-containing CD44v is predominant. When cells undergo EMT, there is a gradual loss of CD44v and gain of the short CD44s isoform, resulting in a nearly complete switch in expression to CD44s in mesenchymal cells. Importantly, this CD44 isoform switching is required for cells to undergo EMT and for the formation of breast tumors that display EMT characteristics in mice. Analysis of breast cancer patient specimens showed that CD44s is up-regulated in high-grade breast tumor tissues and positively correlates with the mesenchymal status of these tumors135. This study demonstrated that cells utilize alternative splicing as a means to regulate EMT by producing a specific CD44 isoform that acts as a key mediator of EMT. Studies on the role of CD44s revealed that CD44s potentiates Akt signaling and promotes cell survival153, an activity that differs from the proliferative advantage mediated by CD44v shown in Author Manuscript Author Manuscript Author Manuscript Author Manuscript Wiley Interdiscip Rev RNA. Author manuscript; available in PMC 2015 May 10. Liu and Cheng Page 8 presence of oxygen, leading to a state that has b.