The anti-cancer drug dabrafenib is not cardiotoxic and inhibits cardiac remodelling and fibrosis in a murine model of hypertension.

Raf kinases signal via extracellular signal-regulated kinases 1/2 (ERK1/2) to drive cell division. Since activating mutations in BRAF (B-Raf proto-oncogene, serine/threonine kinase) are highly oncogenic, BRAF inhibitors including dabrafenib have been developed for cancer. Inhibitors of ERK1/2 signalling used for cancer are cardiotoxic in some patients, raising the question of whether dabrafenib is cardiotoxic. In the heart, ERK1/2 signalling promotes not only cardiomyocyte hypertrophy and is cardioprotective but also promotes fibrosis. Our hypothesis is that ERK1/2 signalling is not required in a non-stressed heart but is required for cardiac remodelling. Thus, dabrafenib may affect the heart in the context of, for example, hypertension. In experiments with cardiomyocytes, cardiac fibroblasts and perfused rat hearts, dabrafenib inhibited ERK1/2 signalling. We assessed the effects of dabrafenib (3 mg/kg/d) on male C57BL/6J mouse hearts in vivo. Dabrafenib alone had no overt effects on cardiac function/dimensions (assessed by echocardiography) or cardiac architecture. In mice treated with 0.8 mg/kg/d angiotensin II (AngII) to induce hypertension, dabrafenib inhibited ERK1/2 signalling and suppressed cardiac hypertrophy in both acute (up to 7 d) and chronic (28 d) settings, preserving ejection fraction. At the cellular level, dabrafenib inhibited AngII-induced cardiomyocyte hypertrophy, reduced expression of hypertrophic gene markers and almost completely eliminated the increase in cardiac fibrosis both in interstitial and perivascular regions. Dabrafenib is not overtly cardiotoxic. Moreover, it inhibits maladaptive hypertrophy resulting from AngII-induced hypertension. Thus, Raf is a potential therapeutic target for hypertensive heart disease and drugs such as dabrafenib, developed for cancer, may be used for this purpose

A Potential Regulatory Role for Intronic microRNA-338-3p for Its Host Gene Encoding Apoptosis-Associated Tyrosine Kinase

MicroRNAs (miRNAs) are important gene regulators that are abundantly expressed in both the developing and adult mammalian brain. These non-coding gene transcripts are involved in post-transcriptional regulatory processes by binding to specific target mRNAs. Approximately one third of known miRNA genes are located within intronic regions of protein coding and non-coding regions, and previous studies have suggested a role for intronic miRNAs as negative feedback regulators of their host genes. In the present study, we monitored the dynamic gene expression changes of the intronic miR-338-3p and miR-338-5p and their host gene Apoptosis-associated Tyrosine Kinase (AATK) during the maturation of rat hippocampal neurons. This revealed an uncorrelated expression pattern of mature miR-338 strands with their host gene. Sequence analysis of the 3′ untranslated region (UTR) of rat AATK mRNA revealed the presence of two putative binding sites for miR-338-3p. Thus, miR-338-3p may have the capacity to modulate AATK mRNA levels in neurons. Transfection of miR-338-3p mimics into rat B35 neuroblastoma cells resulted in a significant decrease of AATK mRNA levels, while the transfection of synthetic miR-338-5p mimics did not alter AATK levels. Our results point to a possible molecular mechanism by which miR-338-3p participates in the regulation of its host gene by modulating the levels of AATK mRNA, a kinase which plays a role during differentiation, apoptosis and possibly in neuronal degeneration

Regulation of expression of contractile proteins with cardiac hypertrophy and failure

Transitions in sarcomeric a-actin and cardiac myosin heavy chain (MHC) gene expression have been useful as molecular markers for the development of cardiac hypertrophy and failure. In simpler model systems, α-actin expression has been useful in delineating some of the molecular pathways responsible for its induction following growth stimulation in vitro. In this study, we report that the effects of adrenergic agonists on α-actin expression in neonatal cardiocytes is dependent upon the culture conditions. In cardiocytes plated at 5 x 10 4 cells/cm 2, skeletal α-actin mRNA levels represent 47%, 37% or 42% of total sarcomeric α-actin accumulations following administrations of 4 μM norepinephrine (NE), isoproterenol (Iso), or phenylephrine (PE), respectively. Cultured cardiocytes treated with vehicle (ascorbate) only accumulated 19% skeletal α-actin. Under these tissue culture conditions, in contrast to data reported previously, skeletal α-actin expression is regulated by both α- and β-adrenergic agonist stimulation. Furthermore, we present data showing that an endogenous anti-β-MHC transcript is regulated by both pressure-overload- or thyroxine-induced cardiac hypertrophy. Although anti-β-MHC transcripts do not play a major role in regulating β-MHC gene expression, the presence of this antisense transcript is associated with a novel set of β-MHC degradation products. In vitro studies, where oligonucleotides complementary to β-MHC have been introduced into cardiomyoctyes, show that the mRNA levels of β-MHC are decreased by 14-21% within 72 h after addition of the oligonucleotides. This result together with the presence of β-MHC degradation products suggest that endogenous anti-β-MHC transcripts may be involved in a post-transcriptional regulatory mechanism affecting the steady-state levels of β-MHC expression.link_to_subscribed_fulltex