Characterization of molecular and cellular functions of the cyclin-dependent kinase CDK9 using a novel specific inhibitor

BACKGROUND AND PURPOSE

The cyclin-dependent kinase CDK9 is an important therapeutic target but currently available inhibitors exhibit low specificity and/or narrow therapeutic windows. Here we have used a new highly specific CDK9 inhibitor, LDC000067 to interrogate gene control mechanisms mediated by CDK9.

EXPERIMENTAL APPROACH

The selectivity of LDC000067 was established in functional kinase assays. Functions of CDK9 in gene expression were assessed with in vitro transcription experiments, single gene analyses and genome-wide expression profiling. Cultures of mouse embryonic stem cells, HeLa cells, several cancer cell lines, along with cells from patients with acute myelogenous leukaemia were also used to investigate cellular responses to LDC000067.

KEY RESULTS

The selectivity of LDC000067 for CDK9 over other CDKs exceeded that of the known inhibitors flavopiridol and DRB. LDC000067 inhibited in vitro transcription in an ATP-competitive and dose-dependent manner. Gene expression profiling of cells treated with LDC000067 demonstrated a selective reduction of short-lived mRNAs, including important regulators of proliferation and apoptosis. Analysis of de novo RNA synthesis suggested a wide ranging positive role of CDK9. At the molecular and cellular level, LDC000067 reproduced effects characteristic of CDK9 inhibition such as enhanced pausing of RNA polymerase II on genes and, most importantly, induction of apoptosis in cancer cells.

CONCLUSIONS AND IMPLICATIONS

Our study provides a framework for the mechanistic understanding of cellular responses to CDK9 inhibition. LDC000067 represents a promising lead for the development of clinically useful, highly specific CDK9 inhibitors.

Ghrelin reduces hepatic mitochondrial fatty acid beta oxidation

Ghrelin is a 28-amino-acid peptide secreted during starvation by gastric cells. Ghrelin physiologically induces food intake and seems to alter lipid and glucid metabolism in several tissues such as adipose tissue and liver. Liver has a key position in lipid metabolism as it allows the metabolic orientation of fatty acids between oxidation and esterification. We investigated the effects of peripheral ghrelin administration on 2 crucial parameters of fatty acid oxidation: the levocarnitine (L-carnitine)-dependent entry of the fatty acids in the mitochondria and the mitochondrial fatty acid oxidation. Ghrelin was either given to rats prior to the hepatocyte preparation and culture or used to treat hepatocytes prepared from control animals. Direct incubation of ghrelin to raw hepatocytes did not induce any change in the studied parameters. In hepatocytes prepared from 3 nmol ghrelin-treated rats, a 44% reduction of the mitochondrial fatty acid oxidation while no alteration of the L-carnitine-related parameters were observed. These results suggested (a) that ghrelin has no direct effect on liver, and (b) that when administrated to a whole organism, ghrelin may alter the lipid metabolism and the energy balance through a marked decrease in liver fatty acid oxidation.

Aging of cylinders excised from pulp tissues of the ;golden delicious' apple

Aging cylinders excised from ;Golden Delicious' apple (Pyrus malus L.) pulp, like the intact fruit, exhibit some characteristic phenomena such as rise in respiration (climacteric), ethylene synthesis, enzymic changes, and increase in ribosomes and mRNA. Aging of cylinders of pulp tissues may offer a useful physiological tool for the study of maturation and senescence.

[Sipple's syndrome: a study through three generations. HLA--carcino-embryonic antigen system. Preliminary results (author's transl)]

Sipple's syndrome in three members of the same family (three successive generations) is reported, confirming that this syndrome is hereditary and transmitted in an autosomal and dominant way. Whereas pheochromocytoma was clinically detectable, medullary thyroïd carcinoma could only be detected in two cases by systematic search for high levels of calcitonin before and after stimulation. In 6 other siblings, thyroïd carcinoma was eliminated in view of negative stimulation tests. HLA groups were studied, but definite conclusions as to the interest of these data in Sipple's syndrome cannot be drawn from 10 few cases. Persistingly high levels of calcitonin after surgery is known to be of severe prognosis; in the present cases, the very short delay after surgery did not allow definite conclusion, since, according to some authors, several months are necessary to allow a return to normal levels.