The catalytic properties of the type II phosphoinositide 5-phosphatases of Lowe's oculocerebrorenal syndrome, INPP5B, Synaptojanin1, Synaptojanin2 and SKIP were analysed with respect to their substrate specificity and enzymological properties. Our data reveal that all phosphatases have unique substrate specificities as judged by their corresponding K M and V Max values. They also possessed an exclusive sensitivity towards fatty acid composition, head group phosphorylation and micellar presentation. Thus, the biological function of these enzymes will not just be determined by their corresponding regulatory domains, but will be distinctly influenced by their catalytic properties as well. This suggests that the phosphatase domains fulfil a unique catalytic function that cannot be fully compensated by other phosphatases.

The tumour suppressor phosphatase and tensin homologue deleted on chromosome 10 (PTEN) shares homology with protein tyrosine phosphatases (PTPases). Similarly, bis-peroxovanadium (bpV) molecules that are well-established PTPase inhibitors were shown to inhibit PTEN, but at up to 100-fold lower concentrations. The preference and potency of the bpVs towards PTEN was validated in vivo as demonstrated by: (i) an increase of Ser473 phosphorylation of protein kinase B (PKB) at similar low nanomolar doses, (ii) the lack of any effect on the PKB phosphorylation in the PTEN negative cell line UM-UC-3, (iii) the ability to rescue Ly294002-induced phosphoinositide 3-kinase inhibition and (iv) a lack of tyrosine phosphorylation at low nanomolar doses.

Phosphatase and tensin homologue deleted on chromosome 10 (PTEN), a phosphoinositide 3-phosphatase, is an important regulator of insulin-dependent signaling. The loss or impairment of PTEN results in an antidiabetic impact, which led to the suggestion that PTEN could be an important target for drugs against type II diabetes. Here we report the design and validation of a small- molecule inhibitor of PTEN. Compared with other cysteine-based phosphatases, PTEN has a much wider active site cleft enabling it to bind the PtdIns(3,4,5)P3 substrate. We have exploited this feature in the design of vanadate scaffolds complexed to a range of different organic ligands, some of which show potent inhibitory activity. A vanadyl complexed to hydroxypicolinic acid was found to be a highly potent and specific inhibitor of PTEN that increases cellular PtdIns(3,4,5)P3 levels, phosphorylation of Akt, and glucose uptake in adipocytes at nanomolar concentrations. The findings presented here demonstrate the applicability of a novel and specific chemical inhibitor against PTEN in research and drug development.

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In spite of the importance of IGF-I for growth and development, knowledge about regulation of its production in submammalian species is rather limited. In order to create a tool for investigation of direct regulatory effects on the expression of IGF-I in bony fish liver, a primary cell culture of hepatocytes from Oreochromis mossambicus, the tilapia, was established. The cells were viable for up to 3 days and IGF-I mRNA synthesis was detected by northern blot and semiquantitative reverse transcriptase (RT)-PCR. Northern blot analysis of the primary cultured hepatocytes revealed four different IGF-I transcripts, 0·5, 1·9, 3·9 and 6·0 kb in size, which were identical to those in liver tissue. However, the expression rate was weaker than that in liver. The direct effects of recombinant tilapia (rt) growth hormone (GH) and salmon (s) IGF-I on the expression of IGF-I in primary cultured hepatocytes were investigated in time-course and doseresponse experiments. In untreated cultures, IGF-I mRNA decreased with time. Hepatocytes treated with 100 nM rtGH resulted in a pronounced stimulation of IGF-I mRNA expression throughout the experiment. Treatment with rtGH in concentrations ranging from 0·1 nM to 1 µM caused a clear dose-dependent increase in the amount of IGF-I mRNA. Significant stimulation was obtained even with 0·1 nM, reaching a plateau with 10 nM. Neither significant inhibitory nor stimulatory effects were detected by adding sIGF-I from 0·1 nM to 1 µM to the hepataocytes. Our results indicate that the established primary cell culture of tilapia hepatocytes is a useful system in which to study direct effects of potential regulators of bony fish liver cell function.