CD9, but not other tetraspans, associates with the β1 integrin precursor

Abstract

The molecules of the tetraspan superfamily have two unequal extracellular domains separated by four transmembrane (TM) domains. These molecules are associated on the cell surface with each other and with other partner molecules, in particular beta1 integrins. We now show that CD9 associates with the precursor of the beta1 integrin (pre beta1). This association is detected as early as 15 min after metabolic labeling, and the use of Brefeldin A demonstrates that it does not require Golgi modifications of either CD9 or integrin beta1. The specificity of this interaction is demonstrated by the fact that other tetraspans, CD63, CD81, and CD82, do not associate with pre beta1, and CD9 does not associate with immature human histocompatibility leukocyte antigen class I. In order to localize the region of CD9 responsible for the association with the beta1 integrin, we have generated two reciprocal chimeric CD9/CD82 molecules with the junction localized just after the third TM region. The large extracellular loop of CD9 or the fourth TM domain, or both, appear to be sufficient to mediate an association with the mature integrin with a high efficiency, compared to CD82. By contrast, association with pre beta1 requires at least two regions of the molecule. Mutation of CD9 at the consensus site of the tetraspan superfamily, localized between the second and the third TM domain, did not impair the co-precipitation of pre beta1. Finally, because pre beta1 associates with calnexin, we have investigated a possible association of CD9 with this chaperone molecule. CD9 associates with calnexin independently of its association with the beta1 integrin, suggesting that calnexin could be involved in the processing of CD9.

Laminin-alpha6beta1 integrin interaction enhances survival and proliferation and modulates steroidogenesis of ovine granulosa cells

“…The 6 integrin subunit was detected as a single band at 120 kDa (Fig. 1A, lanes 3 and 4) and the 1 integrin subunit as two bands corresponding to the mature (125 kDa) and the precursor (110 kDa) forms as previously described (Rubinstein et al 1997) (Fig. 1A, lanes 5 and 6).…”

Direct Extracellular Contact between Integrin α3β1 and TM4SF Protein CD151

“…9) is based primarily on hydrophobicity plots. Also, the extracellular location of the large loop is supported by epitope mapping (48,49) and the presence of sites that undergo N-glycosylation. However, it has yet to be demonstrated that the proposed intracellular amino-and carboxylterminal domains are indeed intracellular.…”

Expression of the Vacuolar H+-ATPase 16-kDa Subunit Results in the Triton X-100-insoluble Aggregation of β1 Integrin and Reduction of Its Cell Surface Expression

“…However, there are several examples where calnexin seems to show chaperone activity toward highly hydrophobic transmembrane proteins, including CD9 (27,28), proteolipid protein (29), and CD82 (30), suggesting a possible role of calnexin in the quality control of transmembrane domain assembly. These studies, taken with our current results, raise the possibility that calnexin may interact with 16K to function in the ER quality control of 16K biosynthesis.…”