Vaccination with human tyrosinase DNA induces antibody responses in dogs with advanced melanoma.

Antitumor immune responses can be elicited in preclinical mouse melanoma models using plasmid DNA vaccines encoding xenogeneic melanosomal differentiation antigens. We previously reported on a phase I clinical trial of human tyrosinase (huTyr) DNA vaccination of 9 dogs with advanced malignant melanoma (World Health Organization stages II-IV), in which we demonstrated the safety of the treatment and the prolongation of the expected survival time (ST) of subjects as compared to historical, stage-matched controls. As a secondary goal of the same study, we report here on the induction of tyrosinase-specific antibody responses in three of the nine dogs vaccinated with huTyr DNA. The antibodies in two of the three responders cross-react with syngeneic canine tyrosinase, demonstrating the ability of this vaccine to overcome host immune tolerance and/or ignorance to or of "self" antigens. Most interestingly, the onset of antibody induction in these three dogs coincides with observed clinical responses and may suggest a means to account for their long-term tumor control and survival.

The cyclin-dependent kinase (CDK) family member PNQALRE/CCRK supports cell proliferation but has no intrinsic CDK-activating kinase (CAK) activity.

The cyclin-dependent kinases (CDKs) that drive the eukaryotic cell cycle must be phosphorylated within the activation segment (T-loop) by a CDK-activating kinase (CAK) to achieve full activity. Although a requirement for CDK-activating phosphorylation is conserved throughout eukaryotic evolution, CAK itself has diverged between metazoans and budding yeast, and fission yeast has two CAKs, raising the possibility that additional mammalian enzymes remain to be identified. We report here the characterization of PNQALRE (also known as CCRK or p42), a member of the mammalian CDK family most similar to the cell-cycle effectors Cdk1 and Cdk2 and to the CAK, Cdk7. Although PNQALRE/CCRK was recently proposed to activate Cdk2, we show that the monomeric protein has no intrinsic CAK activity. Depletion of PNQALRE by >80% due to RNA interference (RNAi) impairs cell proliferation, but fails to arrest the cell cycle at a discrete point. Instead, both the fraction of cells with a sub-G(1) DNA content and cleavage of poly(ADP-ribose) polymerase (PARP) increase. PNQALRE knockdown did not diminish Cdk2 T-loop phosphorylation in vivo or decrease CAK activity of a cell extract. In contrast, depletion of Cdk7 by RNAi causes a proportional decrease in the ability of an extract to activate recombinant Cdk2. Our data do not support the proposed function of PNQALRE/CCRK in activating CDKs, but instead reinforce the notion of Cdk7 as the major, and to date the only, CAK in mammalian cells.