Bovine herpesvirus 1 (BHV-1), an alphaherpesvirus, is a major pathogen that causes respiratory and reproductive infections. We observed tyrosine phosphorylation of a 95-kDa viral protein and dephosphorylation of 55- and 103-kDa cellular proteins during the course of BHV-1 infection. We demonstrated BHV-1 glycoprotein E (gE) to be the tyrosine phosphorylated viral protein by immunoprecipitation. Inhibition of phosphorylation of BHV-1 gE by tyrosine kinase inhibitors genistein and tyrphostin AG1478 substantially lowered the viral titer in Madin-Darby bovine kidney cells. The decrease in viral titer was directly proportional to the decrease in phosphorylation of the BHV-1 gE. Interestingly, these kinase inhibitors did not inhibit the replication of the BHV-1 gE deletion mutant virion (BHV-1gEDelta3.1). Our findings suggest that the wild-type BHV-1, with a functional gE protein, uses a different pathway of signaling events than the BHV-1 gE deletion mutant in replication. Our results indicate that the tyrosine phosphorylation of the cytoplasmic tail of BHV-1 gE is an important post-translational modification of the functional protein. An application of this study may be the use of tyrosine kinase inhibitors in controlling the BHV-1 infection.

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The phosphatidylinositol-3-kinases (PtdIns-3-kinase) are a family of enzymes involved in the control of cell replication. One member of the family, the mammalian p110/p85 PtdIns-3-kinase, is a potential target for anticancer drug development because of its role as a component of growth factor and oncogene activated signalling pathways. There are a number of inhibitors of this PtdIns-3-kinase, the most potent being wortmannin (IC50 4 nM). Wortmannin inhibits cancer cell growth and has shown activity against mouse and human tumor xenografts in mice. Other inhibitors of the PtdIns-3-kinase are halogenated quinones which also inhibit cancer cell growth and have some in vivo antitumor activity. Some D-3-deoxy-3-substituted myo-inositol analogues and their corresponding PtdIns analogues have been synthesized. They may act as myo-inositol antimetabolites in the PtdIns-3-kinase pathway and they can inhibit cancer cell growth.

The improved understanding of oncogenesis and the involvement of oncogenes and tumor suppressor genes, has led to a rational approach of specific target-directed anti-cancer drug development. Cancer genes have been found to be important not only in the control of cell proliferation but also in the mediation of processes such as drug resistance, metastasis, neo-vascularization (angiogenesis), and apoptosis. These are all important targets in their own right and the development of drugs against specific "upstream" targets in oncogenic or growth factor signal transduction cascades it may be possible to inhibit multiple "downstream" targets. Ultimately, to test the hypothesis that signaling pathways offer good targets for anticancer drug development will take several years of careful clinical study and we cannot say at this time whether the approach will work. There are a small number of compounds in the early stages of clinical development as anticancer agents that may act by inhibiting growth factor signaling pathways. In all cases the activity of the compounds on intracellular signaling pathways was discovered after their identification as antiproliferative agents. There are also compounds in preclinical development that have been specifically developed as inhibitors of growth factor signaling, although their selectivity for tumor cells compared to normal tissue remains to be investigated fully in appropriate animal tumor models. It is possible that a single antisignaling drug by itself may not have the power to completely inhibit tumor growth and a combination of drugs may be needed. It may also take a combination of drugs to prevent the emergence of resistance. Clearly there are several challenges to developing this new class of anticancer drugs, and there will undoubtedly be others that must be faced.

A cDNA encoding mouse tyrosinase was inserted into a plasmid containing the provirus of a replication competent avian leukosis virus (ALV). A viral stock produced from the plasmid was used to infect cultured tyrosinase-negative (ca/ca) unpigmented chick embryo melanocytes. Five days after infection many cells were producing very dark discrete melanosomes.