VEGFR-1 Expressed by Malignant Melanoma-Initiating Cells Is Required for Tumor Growth

Abstract

Melanoma growth is driven by malignant melanoma-initiating cells (MMIC) identified by expression of the ATP-binding cassette (ABC) member ABCB5. ABCB5+ melanoma subpopulations have been shown to overexpress the vasculogenic differentiation markers CD144 (VE-cadherin) and TIE1 and are associated with CD31− vasculogenic mimicry (VM), an established biomarker associated with increased patient mortality. Here we identify a critical role for VEGFR-1 signaling in ABCB5+ MMIC-dependent VM and tumor growth. Global gene expression analyses, validated by mRNA and protein determinations, revealed preferential expression of VEGFR-1 on ABCB5+ tumor cells purified from clinical melanomas and established melanoma lines. In vitro, VEGF induced the expression of CD144 in ABCB5+ subpopulations that constitutively expressed VEGFR-1 but not in ABCB5− bulk populations that were predominantly VEGFR-1−. In vivo, melanoma-specific shRNA-mediated knockdown of VEGFR-1 blocked the development of ABCB5+ VM morphology and inhibited ABCB5+ VM-associated production of the secreted melanoma mitogen laminin. Moreover, melanoma-specific VEGFR-1 knockdown markedly inhibited tumor growth (by >90%). Our results show that VEGFR-1 function in MMIC regulates VM and associated laminin production and show that this function represents one mechanism through which MMICs promote tumor growth.

Melanoma stem cells: not rare, but well done

“…Interestingly, CD271 and ABCB5 were recently found to be preferentially coexpressed on the same tumor subpopulation in clinical human melanoma specimens. 75 In another report, a rare subpopulation of melanoma cells identified by high aldehyde dehydrogenase (ALDH) activity displayed enhanced tumorigenicity and capacity for selfrenewal over ALDH-negative cells when serially transplanted into NOD/SCID and IL-2Rg À/À NOD/SCID mice. 76 The existence of a stem cell-like population in melanoma was additionally fortified by a recent study of the effect of the ECM glycoprotein tenascin-C on melanoma progression; these data demonstrated that tenascin-C in the microenvironment encouraged manifestation of a stem cell-like phenotype in melanoma cells that included the expression of ABCB5.…”

“…Moreover, such cells preferentially express vascular endothelial growth factor receptor-1 (VEGFR-1), which was shown via knockdown experimentation to be required for laminin production, VM, and efficient tumor growth in vivo. 75 The current model of signaling pathways involved in VM highlights the dynamic interaction between melanoma cells and their microenvironment. Primitive, aggressive melanoma cells that encourage VM upregulate several endothelialassociated genes, including VE-cadherin (CD144), the receptor protein tyrosine kinase erythropoietin-producing hepatocellular carcinoma-A2 (EphA2), and laminin 5 g2-chain, a major component of the basement membranes.…”

“…In addition, VEGF, a major mediator of tumor angiogenesis, and its receptors may prove to be future targets against VM, as VEGFR-1 has recently been shown to be expressed by ABCB5 þ melanoma cells and required for VM and tumor growth in vivo. 75 Studies in osteosarcoma have demonstrated that VEGF-siRNA silencing suppresses vasculogenic mimicry, inhibits proliferation, and induces apoptosis in vitro. 164 …”

Differential Antitumor Activity of Aflibercept and Bevacizumab in Patient-Derived Xenograft Models of Colorectal Cancer

“…Further evidence correlating VEGFR-1 and the progression of disease was observed in patient-derived xenograft (PDX) models of melanoma, where VEGFR-1 expression on malignant tumor cells was associated with a more aggressive tumor-initiating cell population (25). Other studies with the CT26 colorectal cancer syngeneic mouse model showed that blockade of both VEGFR-1 and VEGFR-2 was required to prevent the vascularization and growth of micrometastases (26).…”

Notch1-MAPK Signaling Axis is Essential in CD133+ Melanoma Initiating Cells

“…The study of tumor initiating cells provides a potential explanation of tumor aggressiveness, drug resistant and distant metastasis [1,2]. Several reports showed that CD133, CD20, CD271, ABCG2 and ABCB5 act as a potential marker to characterize CSCs in melanoma [3,4].…”