Hypoxia-inducible Factor-1-mediated Regulation of Semaphorin 4D Affects Tumor Growth and Vascularity

Abstract

Tumor progression and metastasis depend on the ability of cancer cells to initiate angiogenesis to ensure delivery of oxygen, nutrients, and growth factors to tumor cells and provide access to the systemic circulation. Hypoxia-inducible factor-1 (HIF-1) can activate expression of a broad range of genes that mediate many of the adaptive responses to decreased oxygen concentration, such as enhanced glucose uptake and formation of new blood vessels. Acting through Plexin-B1 on endothelial cells, Semaphorin 4D (Sema4D) has been shown to promote angiogenesis and enhance invasive growth and proliferation in some tumors. Here we show that the gene for Sema4D, the product of which is elevated in head and neck squamous cell carcinoma (HNSCC) cells, contains upstream hypoxia response elements (HRE) and is strongly induced in hypoxia in a HIF-1-dependent manner. Knocking down Sema4D expression with short hairpin (sh) RNA reduces in vitro endothelial cell migration and growth and vascularity of HNSCC xenografts expressing a degradation resistant HIF-1␣ subunit. We also demonstrate a correlation between HIF-1 activity and Sema4D expression in HNSCC specimens. These findings indicate that Sema4D is induced by hypoxia in a HIF-1-dependent manner and influences endothelial cell migration and tumor vascularity. Expression of Sema4D may be a strategy by which carcinomas promote angiogenesis and therefore could represent a therapeutic target for these malignancies.The semaphorins and plexins comprise a family of proteins shown to control proliferation and survival in many different cells and tissues, including the nervous system, the immune system (1), and the vasculature (2). Such diversity of function likely arises as a result of homology with the scatter factor family of proteins, which are known to participate in branching morphogenesis and normal and aberrant motility in numerous cell types (3). Currently, more than 20 semaphorins have been identified that are grouped into eight classes (4). Plexins, which are receptors for the semaphorins, share homology in their extracellular segment with the scatter factor receptors c-Met and RON. In humans, at least nine plexins have been identified and grouped into four families, A through D, most of which have been shown to mediate neuronal cell adhesion and axon guidance (5). We have demonstrated that Semaphorin 4D (Sema4D) 2 is overexpressed by many different aggressive carcinomas, including head and neck squamous cell carcinoma (HNSCC), and that its activity on endothelial cells, which express its receptor Plexin-B1, promotes enhanced growth and vascularity of tumor xenografts in vivo (6). Why Sema4D is overexpressed in so many different tumor types remains unknown, but like other pro-angiogenic factors, plexins and semaphorins may be regulated by changes in oxygen tension (7).The hypoxia-inducible factor-1 (HIF-1) transcriptional complex is the 'master control switch' for hypoxia. Initially identified by Semenza and colleagues in the early 1990s, HIF-1 is composed of two polypeptide...

Ischemic neurons prevent vascular regeneration of neural tissue by secreting semaphorin 3A

“…Although general hypoxia and/or oxidant stress have been shown to affect other semaphorins, 41,42 our study is the first to draw a direct link between the inflammatory stress present in ischemic neural tissue and the induction of semaphorins. Consistent with the theory of segregating damaged areas of tissue, the induction of Sema3A requires prolonged exposure to inflammatory cytokines (here notably IL-1␤), a scenario akin to prolonged exposure to damaging ischemia.…”

“…By 24 hours of hypoxia, VEGF levels subsided, followed at 36 and 48 hours by sharp increases in Sema3A mRNA (P Ͻ .0001; Figure 5A), which is in agreement with hypoxia-and/or oxidant stress-induced regulation of other semaphorins. 41 Accordingly, conditioned medium from hypoxic RGCs taken at 40 hours reduced basal RBMVEC division by 70% (suggestive of cell death; P Ͻ .01), as well as vessel sprouting from aortic explants ( Figure Figure 4. Inhibition of RGC-derived Sema3A during PR preserves neuroretinal function.…”

Inhibition of Semaphorin As a Novel Strategy for Therapeutic Angiogenesis

“…More recently, Sema3A and Sema4A have been shown to inhibit postnatal angiogenesis, 29 suggesting that plexinD1-Fc treatment increases blood flow recovery in ischemic limbs by inhibiting Sema3E but also Sema3A/4A. Sema4D also has an inhibitory effect on postnatal angiogenesis 30 ; however, it remains to be determined whether Sema4D binds to plexinD1.…”

Antibody Blockade of Semaphorin 4D Promotes Immune Infiltration into Tumor and Enhances Response to Other Immunomodulatory Therapies

“…SEMA4D has been reported to inhibit immune-cell migration (12), and its expression may be regulated by hypoxia (13)(14)(15) and other cues within the TME. TAMs have been reported to be a necessary source of SEMA4D within the TME (16).…”