Chronic obstructive pulmonary disease (COPD) is a worldwide threat. Cigarette smoke (CS) exposure causes cardiopulmonary disease and COPD and increases the risk for pulmonary tumors. In addition to poor lung function, patients with COPD are susceptible to bouts of dangerous inflammation triggered by pollutants or infection. These severe inflammatory episodes can lead to additional exacerbations, hospitalization, further deterioration of lung function, and reduced survival. Suitable models of the inflammatory conditions associated with CS, which potentiate the downward spiral in patients with COPD, are lacking, and the underlying mechanisms that trigger exacerbations are not well understood. Although initial CS exposure activates a protective role for vascular endothelial growth factor (VEGF) functions in barrier integrity, chronic exposure depletes the pulmonary VEGF guard function in severe COPD. Thus, we hypothesized that mice with compromised VEGF production and challenged with CS would trigger human-like severe inflammatory progression of COPD. In this model, we discovered that CS exposure promotes an amplified IL-33 cytokine response and severe disease progression. Our VEGF-knockout model combined with CS recapitulates severe COPD with an influx of IL-33-expressing macrophages and neutrophils. Normally, IL-33 is quickly inactivated by a post-translational disulfide bond formation. Our results reveal that BAL fluid from the CS-exposed, VEGF-deficient cohort promotes a significantly prolonged lifetime of active proinflammatory IL-33. Taken together, our data demonstrate that with the loss of a VEGF-mediated protective barrier, the CS response switches from a localized danger to an uncontrolled long-term and long-range, amplified, IL-33-mediated inflammatory response that ultimately destroys lung function.

Although phosphorylation directs serine-arginine (SR) proteins from nuclear storage speckles to the nucleoplasm for splicing function, dephosphorylation paradoxically induces similar movement, raising the question of how such chemical modifications are balanced in these essential splicing factors. In this new study, we investigated the interaction of protein phosphatase 1 (PP1) with the SR protein splicing factor (SRSF1) to understand the foundation of these opposing effects in the nucleus. We found that RNA recognition motif 1 (RRM1) in SRSF1 binds PP1 and represses its catalytic function through an allosteric mechanism. Disruption of RRM1-PP1 interactions reduces the phosphorylation status of the RS domain in vitro and in cells, redirecting SRSF1 in the nucleus. The data imply that an allosteric SR protein-phosphatase platform balances phosphorylation levels in a "goldilocks" region for the proper subnuclear storage of an SR protein splicing factor.

Phosphorylation-dependent cell communication requires enzymes that specifically recognize key proteins in a sea of similar, competing substrates. The protein kinases achieve this goal by utilizing docking grooves in the kinase domain or heterologous protein adaptors to reduce 'off pathway' targeting. We now provide evidence that the nuclear protein kinase CLK1 (cell division cycle2-like kinase 1) important for splicing regulation departs from these classic paradigms by using a novel self-association mechanism. The disordered N-terminus of CLK1 induces oligomerization, a necessary event for targeting its physiological substrates the SR protein (splicing factor containing a C-terminal RS domain) family of splicing factors. Increasing the CLK1 concentration enhances phosphorylation of the splicing regulator SRSF1 (SR protein splicing factor 1) compared with the general substrate myelin basic protein (MBP). In contrast, removal of the N-terminus or dilution of CLK1 induces monomer formation and reverses this specificity. CLK1 self-association also occurs in the nucleus, is induced by the N-terminus and is important for localization of the kinase in sub-nuclear compartments known as speckles. These findings present a new picture of substrate recognition for a protein kinase in which an intrinsically disordered domain is used to capture physiological targets with similar disordered domains in a large oligomeric complex while discriminating against non-physiological targets.