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BCL2 family of apoptosis-related genes: functions and clinical implications in cancer.

One of the most effective ways to combat different types of cancer is through early diagnosis and administration of effective treatment, followed by efficient monitoring that will allow physicians to detect relapsing disease and treat it at the earliest possible time. Apoptosis, a normal physiological form of cell death, is critically involved in the regulation of cellular homeostasis. Dysregulation of programmed cell death mechanisms plays an important role in the pathogenesis and progression of cancer as well as in the responses of tumours to therapeutic interventions. Many members of the BCL2 (B-cell CLL/lymphoma 2; Bcl-2) family of apoptosis-related genes have been found to be differentially expressed in various malignancies, and some are useful prognostic cancer biomarkers. We have recently cloned a new member of this family, BCL2L12, which was found to be differentially expressed in many tumours. Most of the BCL2 family genes have been found to play a central regulatory role in apoptosis induction. Results have made it clear that a number of coordinating alterations in the BCL2 family of genes must occur to inhibit apoptosis and provoke carcinogenesis in a wide variety of cancers. However, more research is required to increase our understanding of the extent to which and the mechanisms by which they are involved in cancer development, providing the basis for earlier and more accurate cancer diagnosis, prognosis and therapeutic intervention that targets the apoptosis pathways. In the present review, we describe current knowledge of the function and molecular characteristics of a series of classic but also newly discovered genes of the BCL2 family as well as their implications in cancer development, prognosis and treatment.

Animals↗

Conservation and divergence of ASK1 and ASK2 gene functions during male meiosis in Arabidopsis thaliana.

Selective proteolysis of regulatory proteins mediated by the ubiquitin pathway is an important mechanism for controlling many biological events. The SCF (Skpl-Cullin-F-box protein) class of E3 ubiquitin ligases controls the ubiquitination of a wide variety of substrates, thereby mediating their degradation by the 26S proteasome. The Arabidopsis genome contains 21 genes encoding Skp1-like proteins that are named as ASKs (Arabidopsis Skp1-like). So far, only the ASK1 gene has been characterized genetically, and is known to be required for male meiosis, flower development, and auxin response. The ASK2 gene is most similar to ASK1 in terms of both the amino acid sequence and expression pattern. To compare ASK2 with ASK1 functionally in male meiosis, different transgenic lines over-expressing ASK1 and ASK2 were tested for their ability to complement the male meiosis defect of the ask1-1 mutant. The genomic ASK1 rescued the ask1-1 mutant defects. The 35S::ASK1 transgene restored male fertility to the ask1-1 mutant, although the percentages of normal pollen grains and tetrads were reduced. 35S::ASK2 lines in the ask1-1 background exhibited partial fertility with even fewer normal pollen grains and tetrads than those of the 35S::ASK1 lines. Detailed analysis of chromosome behavior during male meiosis demonstrated that 35S::ASK1 and 35S::ASK2 lines had different fractions of pollen mother cells undergoing normal meiosis. Our results suggest that ASK2 partially substitutes for ASK1 if expressed at higher than normal levels.

Arabidopsis↗

Finding and decrypting of promoters contributes to the elucidation of gene function.

The combination of full-scale genomic sequencing with high throughput expression analysis provides a new and largely unexploited basis for in silico functional genomics. Recent break through developments in locating and analyzing promoters now allow extending functional genomics in silico far beyond identification of protein sequences into the complex regulatory structures and mechanisms of the genome. However, only first examples of this new type of approach are emerging at present and intensive further developments of bioinformatics tools will be required before such analysis can become large-scale routine in genomic sequence analysis. Nevertheless, the door to a new dimension of functional analysis of the genomic sequence is open. Finally, only the tight integration of the enormous amount of knowledge gained from proteins sequence analysis with the complementary information about gene regulation will afford us with a more complete picture of the networks than constitute life.

Computational Biology↗

A cell system with targeted disruption of the SMN gene: functional conservation of the SMN protein and dependence of Gemin2 on SMN.

The motor neuron degenerative disease spinal muscular atrophy is caused by reduced expression of the survival motor neuron (SMN) protein. Here we report a genetic system developed in the chicken pre-B cell line DT40, in which the endogenous SMN gene is disrupted by homologous recombination, and SMN protein is expressed from a chicken SMN cDNA under control of a tetracycline (tet)-repressible promoter. Addition of tet results in depletion of SMN protein and consequent cell death, which directly demonstrates that SMN is required for cell viability. The tet-induced lethality can be rescued by expression of human SMN, indicating that the function of SMN is highly conserved between the two species. Cells expressing low levels of SMN display slow growth proportional to the amount of SMN they contain. Interestingly, the level of the SMN-interacting protein Gemin2 decreases significantly following depletion of SMN, supporting the conclusion that SMN and Gemin2 form a stable complex in vivo. This system provides a powerful setting for studying the function of SMN in vivo and for screening for potential therapeutics for spinal muscular atrophy.

Amino Acid Sequence↗

Physiological consequences of loss of plasminogen activator gene function in mice.

Indirect evidence suggests a crucial role for the fibrinolytic system and its physiological triggers, tissue-type (t-PA) and urokinase-type (u-PA) plasminogen activator, in many proteolytic processes. Inactivation of the t-PA gene impairs clot lysis and inactivation of the u-PA gene results in occasional fibrin deposition. Mice with combined t-PA and u-PA deficiency suffer extensive spontaneous fibrin deposition, with its associated effects on growth, fertility and survival.

Animals↗

Escherichia coli dnaT gene function is required for pBR322 plasmid replication but not for R1 plasmid replication.

Plasmid pBR322 was unable to replicate in a temperature-sensitive dnaT1 strain at a nonpermissive temperature, whereas a pBR322-derived plasmid carrying the wild-type dnaT+ gene was able to replicate under the same conditions. In contrast to pBR322, plasmid R1 could replicate in the dnaT1 strain at a nonpermissive temperature. In keeping with this finding, in vitro replication of plasmid R1 did not require DnaT protein.

DNA Replication↗

Selective inhibition of interleukin 2 gene function following thymocyte antigen/major histocompatibility complex receptor crosslinking: possible thymic selection mechanism.

Considerable evidence now exists to support the notion that the 50-kDa sheep erythrocyte-binding protein, T11, represents an essential cell surface component of a human T-cell lineage activation pathway. Furthermore, it is known that the human T3-Ti T-cell antigen/major histocompatibility complex receptor complex is capable of regulating cell growth mediated by the T11 structure. Here we show that, within the T3+ thymocyte compartment, T3-Ti crosslinking rapidly inhibits T11-initiated interleukin 2 (IL-2) gene transcription and translation. This inhibition is restricted to the IL-2 gene (IL2) as transcription of both the IL-2-receptor gene (IL2R) and the Ti beta-chain gene (TCRB) are not affected (human gene designations are in parentheses). Perhaps more importantly, T3-Ti-mediated IL-2 inhibition of this type is not operational in peripheral T lymphocytes. The results imply that the majority of T3+ thymocytes are functionally distinct from peripheral T lymphocytes despite their T3+ phenotype and must possess a unique endogenous regulatory component for suppressing IL-2 gene activity. Moreover, since IL-2 is likely rate-limiting for growth within the thymus, the findings provide one plausible mechanism for thymic selection--namely, T3-Ti crosslinking of thymocytes upon interaction with self-major histocompatibility complex inhibits clonal expansion of high-affinity autoreactive cells.

Antigens, Differentiation, T-Lymphocyte↗

Thermosensitive UL9 gene function is required for early stages of herpes simplex virus type 1 DNA synthesis.

DNA replication of herpes simplex virus type 1 (HSV-1) is dependent on a virus-encoded sequence-specific origin-binding protein, the product of the UL9 reading frame. We have identified the mutations in the UL9 gene of three temperature-sensitive (ts) mutants of HSV-1 which are responsible for the ts phenotype (A90T in mutant tsS and V220M in tsR and tsX). The mutations are located in two different conserved helicase sequence motifs of UL9. Two further alterations (I204T and E280D) compared to the published sequence were found in the mutant, revertant and parental wild-type strain 17syn+ sequences and therefore seemed to be irrelevant for the ts phenotype. The ts function of the UL9 protein was required at early times during DNA synthesis whereas upward temperature shifts at later times did not considerably inhibit DNA synthesis.

Amino Acid Sequence↗

Selective inhibition of interleukin 2 gene function following thymocyte antigen/major histocompatibility complex receptor crosslinking: possible thymic selection mechanism.

Considerable evidence now exists to support the notion that the 50-kDa sheep erythrocyte binding protein, T11, represents an essential cell surface component of a human T-cell-lineage activation pathway. Furthermore, it is known that the human T-cell antigen-major histocompatibility complex (MHC) receptor complex T3-Ti is capable of regulating cell growth mediated by the T11 structure. Here we show that, within the T3+ thymocyte compartment, T3-Ti crosslinking rapidly inhibits T11-initiated interleukin 2 (IL-2) gene transcription and translation. This inhibition is restricted to the IL-2 gene (IL2) as transcription of both the IL-2 receptor gene (IL2R) and the Ti beta-chain gene (TCRB) are not affected (human gene designations are in parentheses). Perhaps more importantly, T3-Ti-mediated IL-2 inhibition of this type is not operational in peripheral T lymphocytes. The results imply that the majority of T3+ thymocytes are functionally distinct from peripheral T lymphocytes despite their T3+ phenotype and may possess a unique endogenous regulatory component for suppressing IL-2 gene activity. Moreover, since IL-2 is likely rate-limiting for growth within the thymus, the findings provide one plausible mechanism for thymic selection--namely, T3-Ti crosslinking of thymocytes upon interaction with self-major histocompatibility complex inhibits clonal expansion of high-affinity autoreactive cells.

Antigens, Differentiation, T-Lymphocyte↗