Cell multiplication

Role of RNA-binding protein 5 in the diagnosis and chemotherapeutic response of lung cancer

Lung cancer remains one of the leading causes of cancer-associated mortality in the world. Lung carcinogenesis is frequently associated with deletions or the loss of heterozygosity at the critical chromosomal region 3p21.3, where RNA-binding protein 5 (RBM5) is localized. RBM5 regulates cell growth, cell cycle progression and apoptosis in cell homeostasis. In the lungs, altered RBM5 protein expression leads to alterations in cell growth and apoptosis, with subsequent lung pathogenesis and varied responses to treatment in patients with lung cancer. Detection of RBM5 expression may be a tumor marker for diagnosis, prediction and treatment response in lung cancer, and may be developed as a potential therapeutic target for drug resistant lung cancer. This review discusses the most recent progress on the role of RBM5 in lung cancer.

The phosphorylation of ARPP19 by Greatwall renders the auto-amplification of MPF independently of PKA in Xenopus oocytes

Entry into mitosis or meiosis relies on the coordinated action of kinases and phosphatases that ultimately leads to the activation of Cyclin-B-Cdk1, also known as MPF for M-phase promoting factor. Vertebrate oocytes are blocked in prophase of the first meiotic division, an arrest that is tightly controlled by high PKA activity. Re-entry into meiosis depends on activation of Cdk1, which obeys a two-step mechanism: a catalytic amount of Cdk1 is generated in a PKA and protein-synthesis-dependent manner; then a regulatory network known as the MPF auto-amplification loop is initiated. This second step is independent of PKA and protein synthesis. However, none of the molecular components of the auto-amplification loop identified so far act independently of PKA. Therefore, the protein rendering this process independent of PKA in oocytes remains unknown. Using a physiologically intact cell system, the Xenopus oocyte, we show that the phosphorylation of ARPP19 at S67 by the Greatwall kinase promotes its binding to the PP2A-B55δ phosphatase, thus inhibiting its activity. This process is controlled by Cdk1 and has an essential role within the Cdk1 auto-amplification loop for entry into the first meiotic division. Moreover, once phosphorylated by Greatwall, ARPP19 escapes the negative regulation exerted by PKA. It also promotes activation of MPF independently of protein synthesis, provided that a small amount of Mos is present. Taken together, these findings reveal that PP2A-B55δ, Greatwall and ARPP19 are not only required for entry into meiotic divisions, but are also pivotal effectors within the Cdk1 auto-regulatory loop responsible for its independence with respect to the PKA-negative control.

The antiapoptotic RBM5/LUCA-15/H37 gene and its role in apoptosis and human cancer: research update

The candidate tumour-suppressor gene, LUCA-15/RBM5/H37, maps to the lung cancer tumour-suppressor locus 3p21.3. The LUCA-15 gene locus encodes at least four alternatively spliced transcripts that have been shown to function as regulators of apoptosis, a fact which may have major significance in tumour regulation. This review highlights recent evidence that further implicates the LUCA-15 locus in the control of apoptosis and cell proliferation, and focuses on the observations that confirm the tumour-suppressor activity of this gene.