MET receptor variant R970C favors calpain-dependent generation of a fragment promoting epithelial cell scattering

Recording and classifying MET receptor mutations in cancers

Tyrosine kinase inhibitors (TKI) directed against MET have been recently approved to treat advanced non-small cell lung cancer (NSCLC) harbouring activating MET mutations. This success is the consequence of a long characterization of MET mutations in cancers, which we propose to outline in this review. MET, a receptor tyrosine kinase (RTK), displays in a broad panel of cancers many deregulations liable to promote tumour progression. The first MET mutation was discovered in 1997, in hereditary papillary renal cancer (HPRC), providing the first direct link between MET mutations and cancer development. As in other RTKs, these mutations are located in the kinase domain, leading in most cases to ligand-independent MET activation. In 2014, novel MET mutations were identified in several advanced cancers, including lung cancers. These mutations alter splice sites of exon 14, causing in-frame exon 14 skipping and deletion of a regulatory domain. Because these mutations are not located in the kinase domain, they are original and their mode of action has yet to be fully elucidated. Less than five years after the discovery of such mutations, the efficacy of a MET TKI was evidenced in NSCLC patients displaying MET exon 14 skipping. Yet its use led to a resistance mechanism involving acquisition of novel and already characterized MET mutations. Furthermore, novel somatic MET mutations are constantly being discovered. The challenge is no longer to identify them but to characterize them in order to predict their transforming activity and their sensitivity or resistance to MET TKIs, in order to adapt treatment.

Association of single nucleotide polymorphisms in the CAPN, CAST, LEP, GH, and IGF-1 genes with growth parameters and ultrasound characteristics of the Longissimus dorsi muscle in Colombian hair sheep

Recognition of the genes that influence livestock production characteristics has allowed researchers to identify single nucleotide polymorphisms (SNPs) associated with phenotypic traits that contribute to higher productivity. The objective of this research was to associate SNPs in the genes calpain (CAPN), calpastatin (CAST), leptin (LEP), growth hormone (GH), and insulin-like growth factor 1 (IGF-1) with the growth characteristics birth weight (BW), weaning weight adjusted at 120 days (WW), daily pre-weaning gain (PRADG), adjusted weight at 210 days (AW210), and daily post-weaning gain (POADG), and the measures of the Longissimus dorsi muscle based on ultrasound, namely loin eye area (LEA), loin depth (LD), and back fat thickness (BFT), in Colombian hair sheep (OPC). The association between phenotypic and genotypic characteristics was made using the PLINK v.1.9 program using linear regression analysis. There was a statistically significant association (p < 0.05) between the CAST polymorphism (M/N) and BW, a tendency (p = 0.07) for an association between the T → C SNP of the CAPN gene and AW210, and a trend (p = 0.07) for an association between the A → G SNP of the IGF-1 locus and POADG. The LEA and BFT characteristics were not associated with a SNP, while PL was significantly affected by SNPs in the GH and IGF-1 genes. In conclusion, all the genes evaluated were polymorphic, the CAST gene significantly influenced BW, and the GH and IGF-1 genes were associated with LD characteristics. These results could be used to identify individuals with favorable genotypes to implement a marker-assisted selection method.

Proteolytic Cleavage of Receptor Tyrosine Kinases

The receptor tyrosine kinases (RTKs) are a large family of cell-surface receptors, which are essential components of signal transduction pathways. There are more than fifty human RTKs that can be grouped into multiple RTK subfamilies. RTKs mediate cellular signaling transduction, and they play important roles in the regulation of numerous cellular processes. The dysregulation of RTK signaling is related to various human diseases, including cancers. The proteolytic cleavage phenomenon has frequently been found among multiple receptor tyrosine kinases. More and more information about proteolytic cleavage in RTKs has been discovered, providing rich insight. In this review, we summarize research about different aspects of RTK cleavage, including its relation to cancer, to better elucidate this phenomenon. This review also presents proteolytic cleavage in various members of the RTKs.

Proteolytic cleavages of MET: the divide-and-conquer strategy of a receptor tyrosine kinase

Membrane-anchored full-length MET stimulated by its ligand HGF/SF induces various biological responses, including survival, growth, and invasion. This panel of responses, referred to invasive growth, is required for embryogenesis and tissue regeneration in adults. On the contrary, MET deregulation is associated with tumorigenesis in many kinds of cancer. In addition to its well-documented ligand-stimulated downstream signaling, the receptor can be cleaved by proteases such as secretases, caspases, and calpains. These cleavages are involved either in MET receptor inactivation or, more interestingly, in generating active fragments that can modify cell fate. For instance, MET fragments can promote cell death or invasion. Given a large number of proteases capable of cleaving MET, this receptor appears as a prototype of proteolytic-cleavage-regulated receptor tyrosine kinase. In this review, we describe and discuss the mechanisms and consequences, both physiological and pathological, of MET proteolytic cleavages.

The multiple paths towards MET receptor addiction in cancer

Targeted therapies against receptor tyrosine kinases (RTKs) are currently used with success on a small proportion of patients displaying clear oncogene activation. Lung cancers with a mutated EGFR provide a good illustration. The efficacy of targeted treatments relies on oncogene addiction, a situation in which the growth or survival of the cancer cells depends on a single deregulated oncogene. MET, a member of the RTK family, is a promising target because it displays many deregulations in a broad panel of cancers. Although clinical trials having evaluated MET inhibitors in large populations have yielded disappointing results, many recent case reports suggest that MET inhibition may be effective in a subset of patients with unambiguous MET activation and thus, most probably, oncogene addiction. Interestingly, preclinical studies have revealed a particularity of MET addiction: it can arise through several mechanisms, and the mechanism involved can differ according to the cancer type. The present review describes the different mechanisms of MET addiction and their consequences for diagnosis and therapeutic strategies. Although in each cancer type MET addiction affects a restricted number of patients, pooling of these patients across all cancer types yields a targetable population liable to benefit from addiction-targeting therapies.

Potential Alzheimer's Disease Therapeutics Among Weak Cysteine Protease Inhibitors Exhibit Mechanistic Differences Regarding Extent of Cathepsin B Up-Regulation and Ability to Block Calpain

Cysteine protease inhibitors have long been part of drug discovery programs for Alzheimer's disease (AD), traumatic brain injury (TBI), and other disorders. Select inhibitors reduce accumulating proteins and AD pathology in mouse models. One such compound, Z-Phe-Aladiazomethylketone (PADK), exhibits a very weak IC₅₀ (9-11 μM) towards cathepsin B (CatB), but curiously PADK causes marked up-regulation of the Aβ-degrading CatB and improves spatial memory. Potential therapeutic and weak inhibitor E64d (14 μM IC₅₀) also up-regulates CatB. PADK and E64d were compared regarding the blockage of calcium-induced cytoskeletal deterioration in brain samples, monitoring the 150-kDa spectrin breakdown product (SBDP) known to be produced by calpain. PADK had little to no effect on SBDP production at 10-100 μM. In contrast, E64d caused a dose-dependent decline in SBDP levels with an IC₅₀ of 3-6 μM, closely matching its reported potency for inhibiting μ-calpain. Calpain also cleaves the cytoskeletal organizing protein gephyrin, producing 49-kDa (GnBDP49) and 18-kDa (GnBDP18) breakdown products. PADK had no apparent effect on calcium-induced gephyrin fragments whereas E64d blocked their production. E64d also protected the parent gephyrin in correspondence with reduced BDP levels. The findings of this study indicate that PADK's positive and selective effects on CatB are consistent with human studies showing exercise elevates CatB and such elevation correlates with improved memory. On the other hand, E64d exhibits both marginal CatB enhancement and potent calpain inhibition. This dual effect may be beneficial for treating AD. Alternatively, the potent action on calpain-related pathology may explain E64d's protection in AD and TBI models.

c-Met expression and activity in urogenital cancers - novel aspects of signal transduction and medical implications

C-Met is a receptor tyrosine kinase with multiple functions throughout embryonic development, organogenesis and wound healing and is expressed in various epithelia. The ligand of c-Met is Hepatocyte Growth Factor (HGF) which is secreted among others by mesenchymal stroma/stem (MSC) cells.

Physiological c-Met functions are centred around processes that underly cellular motility and invasive growth. Aberrant c-Met expression and activity is observed in numerous cancers and makes major contributions to cell malignancy. Importantly, HGF/c-Met signaling is crucial in the context of communication between cancer cells and the the tumor stroma.

Here, we review recent findings on roles of dysregulated c-Met in urogenital tumors such as cancers of the urinary bladder, prostate, and ovary. We put emphasis on novel aspects of cancer-associated c-Met expression regulation on both, HGF-dependent and HGF-independent non-canonical mechanisms. Moreover, this review focusses on c-Met-triggered signalling with potential relevance for urogenital oncogenesis, and on strategies to specifically inhibit c-Met activity.