Publications

The cytoplasmic domains of integrin beta subunits are essential for the function of integrins in cell adhesion and signaling. A chimera combining the transmembrane and cytoplasmic domains of the beta 1 integrin subunit with an irrelevant extracellular domain derived from L3T4 (murine CD4) was tested for its ability to interfere with integrin function. Expression of this construct in cultured human embryonic kidney cells under the control of the inducible metallothionein promoter resulted in cell rounding and detachment, and blocked cell adhesion mediated by the beta 1 and alpha v beta 5 integrins. Expression of the beta 1 chimera at basal levels interfered with the tyrosine phosphorylation of a 125-kDa protein induced by antibody-induced clustering of integrins. Induced expression of the chimera resulted in sustained tyrosine phosphorylation of this protein, which could be enhanced by clustering of the chimera but was insensitive to clustering of integrins. These results demonstrate that the autonomously expressed beta 1 integrin cytoplasmic domain can act as a trans-dominant inhibitor of integrin function, presumably via competitive interactions with cytoplasmic components that are required for integrin-mediated cell adhesion and tyrosine phosphorylation.

Cannabidiol (CBD) has been shown to be a selective inactivator of cytochromes P450 (P450s) 2C and 3A in the mouse and, like many P450 inactivators, it can also induce P450s after repeated administration. The inductive effects of CBD on mouse hepatic P450s 2B, 3A, and 2C were determined using cDNA probes, polyclonal antibodies, and specific functional markers. P450 2B10 mRNA was increased markedly after repeated CBD administration and correlated well with increased P450 2B immunoquantified content and functional activity. On the other hand, although the 2-fold increase in P450 3A mRNA detected after repeated CBD administration was consistent with the increased immunoquantified P450 3A protein content, the lack of an observable increase in P450 3A-specific functional activity suggested subsequent inactivation of the induced P450 3A. Repeated CBD treatment increased P450 2C mRNA content 2-fold, but did not increase either the P450 2C immunoquantified content or its functional activity. The effect of CBD treatment on the ability of tetrahydrocannabinol (THC) to induce P450 2B was also determined. A THC dose that did not induce P450 2B significantly was administered alone or in combination with a CBD dose that markedly inactivated P450s 2C- and 3A but submaximally increased P450 2B functional activity. The combination of THC and CBD did not increase P450 2B-catalyzed activity significantly over that observed after CBD treatment alone. Thus, prior CBD-mediated P450 inactivation does not appear to increase the ability of THC to induce P450 2B. To further characterize the relationship between P450 inactivation and induction, several structurally diverse CBD analogs with varying P450 inactivating potentials were tested for their ability to induce P450 2B. At least one CBD analog that is an effective P450 inactivator failed to induce P450 2B, while at least one CBD analog that is incapable of inactivating P450 was found to be a very good P450 2B inducer. It therefore appears that inherent structural features of the CBD molecule rather than its ability to inactivate P450 determine P450 2B inducibility. The complex effects of CBD treatment on P450 inactivation and induction have the potential to influence the pharmacological action of many clinically important drugs known to be metabolized by these various P450s. The mechanism of CBD-mediated P450 induction remains to be elucidated but does not appear to be related to CBD-mediated P450 inactivation.