Phosphatidylinositol 3-kinases (PI3Ks) evolved from a single enzyme that regulates vesicle trafficking in unicellular eukaryotes into a family of enzymes that regulate cellular metabolism and growth in multicellular organisms. In this review, we examine how the PI3K pathway has evolved to control these fundamental processes, and how this pathway is in turn regulated by intricate feedback and crosstalk mechanisms. In light of the recent advances in our understanding of the function of PI3Ks in the pathogenesis of diabetes and cancer, we discuss the exciting therapeutic opportunities for targeting this pathway to treat these diseases.

The evolution of phosphatidylinositol 3-kinases as regulators of growth and metabolism

The phosphoinositide 3-kinase (PI3K) pathway is a key signal transduction system that links oncogenes and multiple receptor classes to many essential cellular functions, and is perhaps the most commonly activated signalling pathway in human cancer. This pathway therefore presents both an opportunity and a challenge for cancer therapy. Even as inhibitors that target PI3K isoforms and other major nodes in the pathway, including AKT and mammalian target of rapamycin (mTOR), reach clinical trials, major issues remain. Here, we highlight recent progress that has been made in our understanding of the PI3K pathway and discuss the potential of and challenges for the development of therapeutic agents that target this pathway in cancer.

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Targeting the phosphoinositide 3-kinase pathway in cancer.

The most recently discovered PTEN tumor suppressor gene has been found to be defective in a large number of human cancers. In addition, germ-line mutations in PTEN result in the dominantly inherited disease Cowden syndrome, which is characterized by multiple hamartomas and a high proclivity for developing cancer. A series of publications over the past year now suggest a mechanism by which PTEN loss of function results in tumors. PTEN appears to negatively control the phosphoinositide 3-kinase signaling pathway for regulation of cell growth and survival by dephosphorylating the 3 position of phosphoinositides.

https://www.pnas.org/content/pnas/96/8/4240.full.pdf

New insights into tumor suppression: PTEN suppresses tumor formation by restraining the phosphoinositide 3-kinase/AKT pathway

Plant Molecular Biology Manual (Second Edition) is an entirely new manual containing both fundamental and recently described techniques in the area of plant molecular biology. Designed for use in the research laboratory, the Plant Molecular Biology Manual presents detailed techniques in the areas of plant transformation, recombinant DNA and other nucleic acid manipulations, nuclear run-on and in vitro transcription systems, in situ hybridization and immunodetection systems, protein-nucleic acid interaction analyses, subcellular targeting of proteins in the plant cell, and gene tagging using T-DNA and transposons. This second edition contains more than 40 newly written chapters, including descriptions of subjects such as virus-mediated gene transfer, specialized Agrobacterium strains and T-DNA vectors, nuclear run-on and in vitro transcription systems, non-radioactive detection systems, characterization of transcription factors, nuclear protein targeting, and T-DNA and transposon mutagenesis, not previously described in the first edition.

Plant Molecular Biology Manual

The PTEN gene encodes a dual-specificity phosphatase mutated in a variety of human cancers. PTEN germline mutations are found in three related human autosomal dominant disorders, Cowden disease (CD), Lhermitte-Duclos disease (LDD) and Bannayan-Zonana syndrome (BZS), characterized by tumour susceptibility and developmental defects. To examine the role of PTEN in ontogenesis and tumour suppression, we disrupted mouse Pten by homologous recombination. Pten inactivation resulted in early embryonic lethality. Pten-/- ES cells formed aberrant embryoid bodies and displayed an altered ability to differentiate into endodermal, ectodermal and mesodermal derivatives. Pten+/- mice and chimaeric mice derived from Pten+/- ES cells showed hyperplastic-dysplastic changes in the prostate, skin and colon, which are characteristic of CD, LDD and BZS. They also spontaneously developed germ cell, gonadostromal, thyroid and colon tumours. In addition, Pten inactivation enhanced the ability of ES cells to generate tumours in nude and syngeneic mice, due to increased anchorage-independent growth and aberrant differentiation. These results support the notion that PTEN haploinsufficiency plays a causal role in CD, LDD and BZS pathogenesis, and demonstrate that Pten is a tumour suppressor essential for embryonic development.

Pten is essential for embryonic development and tumour suppression.

We have significantly improved a method originally developed by Liang and Pardee [Science 257 (1992) 967-971] to display a broad spectrum of expressed genes and to detect differences in expression between different cell types. We have analysed various aspects of the technique and have modified it for both, the application to fast and efficient identification of genes and the use with automatic analysis systems. Based on the mathematical background we have devised the appropriate number of optimal PCR primers. We have also introduced nondenaturating gels for separating double stranded fragments as single bands. By applying the method to regenerating mouse liver, we have identified, out of a total of 38,000 bands, about 70 fragments where the expression of the corresponding genes seems to be differentially regulated at different time points. Application of the method to an automatic DNA sequencer was successfully done. Thus, we have confirmed the usefulness and increased the power of the RNA display technique, which we named differential display reverse transcription PCR (DDRT-PCR), and have extended the range of its application.

Identification of differentially expressed mRNA species by an improved display technique (DDRT-PCR).

The MMAC1/PTEN gene, located at 10q23.3, is a candidate tumor suppressor commonly mutated in glioma. We have studied the pattern of deletion, mutation, and expression of MMAC1/PTEN in 35 unrelated melanoma cell lines. Nine (26%) of the cell lines showed partial or complete homozygous deletion of the MMAC1/PTEN gene, and another six (17%) harbored a mutation in combination with loss of the second allele. Mutations could also be demonstrated in uncultured tumor specimens from which the cell lines had been established, and cell lines derived from two different metastases from one individual carried the same missense mutation. Collectively, these findings suggest that disruption of MMAC1/PTEN by allelic loss or mutation may contribute to the pathogenesis or neoplastic evolution in a large proportion of malignant melanomas.

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Disruption of the MMAC1/PTEN Gene by Deletion or Mutation Is a Frequent Event in Malignant Melanoma

Somatic Fas Mutations in Non-Hodgkin's Lymphoma: Association With Extranodal Disease and Autoimmunity

Mutation and Allelic Loss of the PTEN/MMAC1 gene in Primary and Metastatic Melanoma Biopsies

Mutations in LKB1/STK11, a gene mapping to chromosome 19p13.3 and encoding a widely expressed serine/threonine kinase, were recently identified as the cause of Peutz-Jeghers syndrome. Despite the hamartomatous polyps and increased cancer risk associated with this syndrome, somatic alterations in LKB1/STK11 have not been identified in human tumours. Prompted by another feature of the syndrome, lentigines of the lips and oral mucosa, we evaluated the status of LKB1/STK11 expression, deletion, and mutation in cell lines and tumour samples from 35 patients with sporadic malignant melanoma. Two somatic mutations were identified, a nonsense mutation (Glu170Stop) causing exon skipping and intron retention, and a missense mutation (Asp194Tyr) affecting an invariant residue in the catalytic subunit of LKB1/STK11. Our data suggest that LKB1/STK11 may contribute to tumorigenesis in a small fraction of malignant melanomas.

Vibeke Ahrenkiel

Papers

Identification of differentially expressed mRNA species by an improved display technique (DDRT-PCR).

Disruption of the MMAC1/PTEN Gene by Deletion or Mutation Is a Frequent Event in Malignant Melanoma

Somatic Fas Mutations in Non-Hodgkin's Lymphoma: Association With Extranodal Disease and Autoimmunity

Mutation and Allelic Loss of the PTEN/MMAC1 gene in Primary and Metastatic Melanoma Biopsies

Somatic mutation of the Peutz-Jeghers syndrome gene, LKB1/STK11, in malignant melanoma.