Filamin protects myofibrils from contractile damage through changes in its mechanosensory region.

Filamins are mechanosensitive actin crosslinking proteins that organize the actin cytoskeleton in a variety of shapes and tissues. In muscles, filamin crosslinks actin filaments from opposing sarcomeres, the smallest contractile units of muscles. This happens at the Z-disc, the actin-organizing center of sarcomeres. In flies and vertebrates, filamin mutations lead to fragile muscles that appear ruptured, suggesting filamin helps counteract muscle rupturing during muscle contractions by providing elastic support and/or through signaling. An elastic region at the C-terminus of filamin is called the mechanosensitive region and has been proposed to sense and counteract contractile damage. Here we use molecularly defined mutants and microscopy analysis of the Drosophila indirect flight muscles to investigate the molecular details by which filamin provides cohesion to the Z-disc. We made novel filamin mutations affecting the C-terminal region to interrogate the mechanosensitive region and detected three Z-disc phenotypes: dissociation of actin filaments, Z-disc rupture, and Z-disc enlargement. We tested a constitutively closed filamin mutant, which prevents the elastic changes in the mechanosensitive region and results in ruptured Z-discs, and a constitutively open mutant which has the opposite elastic effect on the mechanosensitive region and gives rise to enlarged Z-discs. Finally, we show that muscle contraction is required for Z-disc rupture. We propose that filamin senses myofibril damage by elastic changes in its mechanosensory region, stabilizes the Z-disc, and counteracts contractile damage at the Z-disc.

Outcomes of Rural Men with Breast Cancer: A Multicenter Population Based Retrospective Cohort Study.

BACKGROUND: Breast cancer is rare in men. This population-based study aimed to determine outcomes of male breast cancer in relation to residence and other variables. METHODS: In this retrospective cohort study, men diagnosed with breast cancer in Saskatchewan during 2000-2019 were evaluated. Cox proportional multivariable regression analyses were performed to determine the correlation between survival and clinicopathological and contextual factors. RESULTS: One hundred-eight eligible patients with a median age of 69 years were identified. Of them, 16% had WHO performance status ≥ 2 and 61% were rural residents. The stage at diagnosis was as follows: stage 0, 7%; I, 31%; II, 42%; III, 11%; IV, 8%. Ninety-eight percent had hormone receptor-positive breast cancer. The median disease-free survival of urban patients was 97 (95% CI: 50-143) vs. 64 (46-82) months of rural patients (p = 0.29). The median OS of urban patients was 127 (94-159) vs. 93 (32-153) months for rural patients (p = 0.27). On multivariable analysis, performance status ≥ 2, hazard ratio (HR) 2.82 (1.14-6.94), lack of adjuvant systemic therapy, HR 2.47 (1.03-5.92), and node-positive disease, HR 2.32 (1.22-4.40) were significantly correlated with inferior disease-free survival in early-stage invasive breast cancer. Whereas stage IV disease, HR 7.8 (3.1-19.5), performance status ≥ 2, HR 3.25 (1.57-6.71), and age ≥ 65 years, HR 2.37 (1.13-5.0) were correlated with inferior overall survival in all stages. CONCLUSIONS: Although residence was not significantly correlated with outcomes, rural men had numerically inferior survival. Poor performance status, node-positive disease, and lack of adjuvant systemic therapy were correlated with inferior disease-free survival.

The unexpected versatility of ALP/Enigma family proteins.

One of the most intriguing features of multicellular animals is their ability to move. On a cellular level, this is accomplished by the rearrangement and reorganization of the cytoskeleton, a dynamic network of filamentous proteins which provides stability and structure in a stationary context, but also facilitates directed movement by contracting. The ALP/Enigma family proteins are a diverse group of docking proteins found in numerous cellular milieus and facilitate these processes among others. In vertebrates, they are characterized by having a PDZ domain in combination with one or three LIM domains. The family is comprised of CLP-36 (PDLIM1), Mystique (PDLIM2), ALP (PDLIM3), RIL (PDLIM4), ENH (PDLIM5), ZASP (PDLIM6), and Enigma (PDLIM7). In this review, we will outline the evolution and function of their protein domains which confers their versatility. Additionally, we highlight their role in different cellular environments, focusing specifically on recent advances in muscle research using Drosophila as a model organism. Finally, we show the relevance of this protein family to human myopathies and the development of muscle-related diseases.

Slik phosphorylation of Talin T152 is crucial for proper Talin recruitment and maintenance of muscle attachment in Drosophila.

Talin is the major scaffold protein linking integrin receptors with the actin cytoskeleton. In Drosophila, extended Talin generates a stable link between the sarcomeric cytoskeleton and the tendon matrix at muscle attachment sites. Here, we identify phosphorylation sites on Drosophila Talin by mass spectrometry. Talin is phosphorylated in late embryogenesis when muscles differentiate, especially on T152 in the exposed loop of the F1 domain of the Talin head. Localization of a mutated version of Talin (Talin-T150/T152A) is reduced at muscle attachment sites and can only partially rescue muscle attachment compared with wild-type Talin. We also identify Slik as the kinase phosphorylating Talin at T152. Slik localizes to muscle attachment sites, and the absence of Slik reduces the localization of Talin at muscle attachment sites causing phenotypes similar to Talin-T150/T152A. Thus, our results demonstrate that Talin phosphorylation by Slik plays an important role in fine-tuning Talin recruitment to integrin adhesion sites and maintaining muscle attachment.