CD9-mediated activation of the p46 Shc isoform leads to apoptosis in cancer cells

Abstract

CD9, a member of the tetraspanin family, has been shown to be involved in a range of cellular activities, including migration, proliferation and adhesion, but the molecular mechanisms by which it mediates such events is unclear. Here, we found that anti-CD9 monoclonal antibody ALB6 inhibited cell proliferation, reduced cell viability and induced not only morphological changes specific to apoptosis but also molecular changes, as evidenced by TUNEL and annexin-V staining. For the possible mechanism of ALB6-induced apoptosis, ALB6 activated the c-Jun NH2-terminal kinase/stress-activated protein kinase (JNK/SAPK) and p38 mitogen-activated-protein kinase (MAPK) within 5-15 minutes, as well as caspase-3 within 24-48 hours. It is noteworthy that ALB6 induced tyrosine phosphorylation of the p46 Shc isoform specifically and that the overexpression of its dominant-negative form completely suppressed the ALB6-induced activation of JNK/SAPK, p38 MAPK and caspase-3, resulting in the inhibition of apoptotic cell death. These results suggest that CD9 might regulate apoptosis through the specialized signals in human cancer cell lines.

Tetraspanins Regulate ADAM10-Mediated Cleavage of TNF-α and Epidermal Growth Factor

“…Tetraspanins have been shown to be coupled to diverse signal transduction pathways, including PKC, tyrosine kinases, and the MAPK pathways (44,(63)(64)(65)(66)(67). As expected, the PKC inhibitor bisindolylmaleimide I blocked the release of TNF-␣ induced by the PKC activator TPA.…”

“…We have shown here that the increased TNF-␣ release induced by the CD82 mAb is dependent on an intact MEK/Erk pathway, but does not depend on the p38 MAPK pathway. Although the engagement of tetraspanins has been shown to activate these pathways in nonhematopoietic cell lines (66,67), the stimulation of ADAM10-mediated TNF-␣ shedding by anti-tetraspanin mAbs is not a mere consequence of the activation of the Erk pathway. Indeed, we did not observe Erk activation upon addition of CD82 mAb to Raji cells although TPA caused strong Erk phosphorylation without inducing ADAM10-mediated TNF-␣ shedding.…”

Tetraspanin CD9 participates in dysmegakaryopoiesis and stromal interactions in primary myelofibrosis

“…Indeed, by regulating the apoptotic process, targeting CD9 may improve the dysmegakaryopoiesis that characterizes PMF, as demonstrated in human cancer cells. 44 In the same way, the role of the Akt pathway driven by CD9 in PMF megakaryocytes is consistent with the findings of a recent study that established Akt as a rational therapeutic target for the treatment of patients with myeloproliferative neoplasms. 45 In brief, our results indicate original therapeutic avenues targeting hematopoietic cell-stroma interactions in PMF.…”

The C-terminal tail of tetraspanin protein CD9 contributes to its function and molecular organization

“…CD9 has tumor-suppressor-like functions in many tumor cell types, and can inhibit cell invasion and metastasis (Ikeyama et al, 1993;Zoller, 2009). CD9 also contributes to cell signaling (Huang et al, 2004), and can regulate cell adhesion (Masellis-Smith and Shaw, 1994), migration (Anton et al, 1995), apoptosis (Murayama et al, 2004), membrane protein shedding (Shi et al, 2000) and diphtheria toxin binding (Iwamoto et al, 1994). To assist in these diverse functions, CD9 interacts directly with transmembrane proteins EWI-2 (Charrin et al, 2003;Stipp et al, 2001a) and EWI-F (also called CD9P-1 and FPRP) (Charrin et al, 2001;Stipp et al, 2001b).…”