Downregulation of CD9 promotes pancreatic cancer growth and metastasis through upregulation of epidermal growth factor on the cell surface

Abstract

The expression of CD9 has been shown to be inversely associated with pancreatic cancer metastasis but the underlying mechanism remains incompletely understood. Using the two closely associated pancreatic cancer cell lines, PaTu-8898s and PaTu-8898t, which are metastatic and non-metastatic, respectively, we showed that the PaTu-8988s cells expressed a lower level of CD9 but had higher proliferation and migration rates than the PaTu-8898t cells. An inverse correlation between CD9 expression and the cell surface level of epidermal growth factor receptor (EGFR) was observed in both cell lines. In the PaTu-8898s cells, overexpression of CD9 decreased the cell surface expression of EGFR, associated with increased expression of dynamin-2, whereas in the PaTu-8898t cells, knockdown of CD9 with RNA interference (RNAi) increased the cell surface expression of EGFR, associated with decreased expression of dynamin-2. However, the total EGFR level did not change by manipulation of CD9 expression, suggesting that CD9 plays a role in EGFR endocytosis. Furthermore, in the PaTu-8898ts cells, CD9 overexpression decreased the cell proliferation and migration, which were reversed by EGFR overexpression, whereas in the PaTu-8898t cells, CD9 knockdown enhanced the cell proliferation and migration which were blocked by EGFR RNAi both in vitro and in vivo. Thus, in pancreatic cancer cells, downregulation of CD9 may play a role in cancer growth and metastasis through, at least in part, enhancing cell surface expression of EGFR.

ErbB receptors and tetraspanins: Casting the net wider

“…A steady-state level of EGFR was negatively regulated by CD9, and antibody-induced ligation of CD9 facilitated ligand-induced endocytosis of the receptor (7; 10). The surface clearance of EGFR was linked to CD9-dependent regulation of the expression of dynamin-2, a critical component of various endocytic pathways (10). Ligand-induced phosphorylation of EGFR and its partner adaptor protein Shc was decreased in CD9-expressing cells when compared to control, and CD9 was also shown to attenuate EGFR-induced activation of PI3-kinase and MAPK/Erk pathways (7; 11).…”

Expression of CD9 and CD82 in papillary thyroid microcarcinoma and its prognostic significance

“…There are also some studies about other mechanisms that CD9 is involved in in various cancer cells. One study reported that downregulation of CD9 in pancreatic cancer cells induces upregulation of the epidermal growth factor, thereby promoting cancer cell growth and metastasis [31]. In ovarian cancer, upregulation of CD9 is related to the induction of TNF-a gene expression and constitutive NF-kB activation [32].…”

Tetraspanins, More than Markers of Extracellular Vesicles in Reproduction

“…The tetraspanin family includes distinct proteins characterized by their common specific molecular structure ( Figure 2 ), represented by four transmembrane domains containing conserved polar residues; a small extracellular loop (SEL) and large extracellular loop (LEL) with 4, 6, 7 or 8 conserved cysteine residues; and short cytoplasmic tails [ 44 , 45 , 46 , 47 , 48 ]. Polar residues stabilize the tertiary structure [ 49 ]. Tetraspanins are usually post-translationally modified by glycosylation in extracellular domains and palmitoylation at intracellular cysteines [ 43 ].…”

“…Moreover, tetraspanins can associate with lipids (e.g., cholesterol), creating larger complexes [ 43 ]. It was shown that the constant region of the LEL is responsible for tetraspanin dimerization, while the variable region is responsible for the association with non-tetraspanin partners [ 49 ]. In general, tetraspanins are implicated in many cellular processes, such as cell adhesion [ 55 ], regulation of cell motility, and/or morphology, fusion, signaling, and other functions [ 52 , 56 , 57 , 58 , 59 ].…”