Anp32e/Cpd1 regulates protein phosphatase 2A activity at synapses during synaptogenesis.

Anp32e/Cpd1, a member of the acidic nuclear phosphoprotein (Anp)32 family, is characterized by the presence of an amino terminal domain containing four leucine-rich repeats and a carboxyl-terminal low-compositional complexity acidic region. In previous studies performed to understand the biological role of Anp32e/Cpd1, we showed a predominant presence of Anp32e/Cpd1 in the nucleus. However, when Anp32e/Cpd1 is in the cytoplasm, it co-localizes spatially with protein phosphatase 2A (PP2A) near cell membranes, far from the synapses. In the present work, we show that Anp32e/Cpd1 is also present as a membrane-bound 74/76-kDa protein with a widespread distribution in the brain. We reveal that the expression, synthesis and half-life of this high-molecular-weight form of Anp32e/Cpd1 are spatially and temporally correlated with the cerebellar synaptogenesis period. We demonstrate that synaptic Anp32e/Cpd1 co-localizes, interacts and inhibits PP2A activity, and that phosphorylation of Anp32/Cpd1 is required for the Anp32e-PP2A interaction. Also, subcellular localization was shown with electronic microscopy. Finally, we examine Anp32e/Cpd1 and PP2A distribution in two ataxic mutant models, weaver and staggerer, and show that their co-localization in Purkinje cell dendrites depends on parallel fibre/Purkinje cell contacts. Based on these observations, we propose that Anp32e/Cpd1 mediates synaptogenesis process by modulating PP2A activity.

Correlation between synaptogenesis and the PTEN phosphatase expression in dendrites during postnatal brain development.

The PTEN (phosphatase and tensin homolog deleted on chromosome 10) tumor suppressor gene codifies a lipid inositol 3'-phosphatase that negatively regulates cell survival mediated by the phosphatidyl inositol 3' kinase (PIP3-kinase)--protein kinase B/Akt signaling pathway. Recently, PIP3-kinase was involved in axon polarization, but PTEN functions in dendrites are uncertain. Using amino-terminal antibodies against the catalytic domain, we found a 34 kDa fragment of PTEN protein detected only in mouse brain tissue, present in neuron dendrites and spines of cerebral cortex, cerebellum, hippocampus and olfactory bulb. The PTEN-fragment reaches the synaptic fraction with a positive temporal correlation with synaptic stabilization in postnatal cerebellum and brain. In the weaver mutant mice, PTEN was absent only in the Purkinje cells dendrites that cannot receive the granule cells synaptic input. Furthermore, the activated p-Akt/PKB was present in axons but not in dendrites of mature neuron cells. P-Akt was also altered by the weaver mutation maintaining the inverse correlation with the PTEN-fragment in Purkinje cell dendrites. In contrast, the expression of this fragment was not affected by the staggerer mutation. Together, these results suggest that synaptogenesis is a necessary process for polarization in PIP3 pathway mediated by the PTEN catalytic-fragment into dendrites of CNS neurons.

Roscovitine inhibits ongoing DNA synthesis in human cervical cancer.

The effect of roscovitine, a purine analogue and cyclin dependent kinase inhibitor, on DNA synthesis rate in tissue mini-units obtained from human cervical cancers was investigated. Roscovitine (100 microM) gave a DNA synthesis rate inhibition by 61% (P<0.0001; range 23-93%) within 30 min of incubation. This inhibitory effect was concentration-dependent. The results suggest that the inhibition of tumor DNA synthesis rate is due to a direct effect on the DNA synthesis machinery via presently unknown mechanisms. In addition, the potential application of CDKs inhibitors as preventive agents is discussed.