ABSTRACT
The Rho family of small GTPases control cell migration, cell invasion and cell cycle. Many of these processes are perturbed in cancer and several family members show altered expression in a number of tumor types. RhoBTB2/DBC2 is an atypical member of this family of signaling proteins, containing two BTB domains in addition to its conserved Rho GTPase domain. RhoBTB2 is mutated, deleted or silenced in a large percentage of breast and lung cancers; however, the functional consequences of this loss are unclear. Here we use RNA interference in primary human epithelial cells to mimic the loss of RhoBTB2 seen in cancer cells. Through microarray analysis of global gene expression, we show that loss of RhoBTB2 results in downregulation of CXCL14-a chemokine that controls leukocyte migration and angiogenesis, and whose expression is lost through unknown mechanisms in a wide range of epithelial cancers. Loss of RhoBTB2 expression correlates with loss of CXCL14 secretion by head and neck squamous cell carcinoma cell lines, whereas reintroduction of RhoBTB2 restores CXCL14 secretion. Our studies identify CXCL14 as a gene target of RhoBTB2 and support downregulation of CXCL14 as a functional outcome of RhoBTB2 loss in cancer.
Subject(s)
Chemokines, CXC/genetics , GTP-Binding Proteins/physiology , Neoplasms/genetics , Neoplasms/physiopathology , Tumor Suppressor Proteins/physiology , Carcinoma, Squamous Cell/genetics , Cell Cycle/physiology , Cell Line, Tumor , Cell Movement/physiology , Conserved Sequence , Cullin Proteins/genetics , GTP-Binding Proteins/deficiency , GTP-Binding Proteins/genetics , Gene Expression Regulation, Neoplastic , Gene Silencing , HeLa Cells , Head and Neck Neoplasms/genetics , Humans , Leukocytes/physiology , Neoplasm Invasiveness/physiopathology , Neoplasms/blood supply , Neovascularization, Pathologic/genetics , Reference Values , Signal Transduction , Tumor Suppressor Proteins/deficiency , Tumor Suppressor Proteins/geneticsABSTRACT
The development of an altered stromal microenvironment is a common feature of many tumours including squamous cell carcinoma (SCC), and there is increasing evidence that these changes in the stroma, which include increased expression of proteases and cytokines, may actually promote tumour progression. A common finding is that stromal fibroblasts become 'activated' myofibroblasts, expressing smooth muscle actin and secreting cytokines, proteases and matrix proteins. We show that myofibroblasts are commonly found in the stroma of oral SCC and are often concentrated at the invasive margin of the tumour. Using oral SCC cells and primary oral fibroblasts, we demonstrate that tumour cells directly induce a myofibroblastic phenotype, and that this transdifferentiation is dependent on SCC-derived TGF-beta1. In turn, myofibroblasts secrete significantly higher levels of hepatocyte growth factor/scatter factor compared with fibroblast controls, and this cytokine promotes SCC invasion through Matrigel, a mixture of basement membrane proteins. This is the first time that this double paracrine mechanism has been demonstrated between squamous carcinoma cells and fibroblasts, and emphasises that cancer invasion can be promoted indirectly by the release of tumour-induced host factors from stroma.
