Summary The primary cilium acts as a transducer of extracellular stimuli into intracellular signaling [1, 2]. Its regulation, particularly with respect to length, has been defined primarily by genetic experiments and human disease states in which molecular components that are necessary for its proper construction have been mutated or deleted [1]. However, dynamic modulation of cilium length, a phenomenon observed in ciliated protists [3, 4], has not been well-characterized in vertebrates. Here we demonstrate that decreased intracellular calcium (Ca2+) or increased cyclic AMP (cAMP), and subsequent PKA activation, increases primary cilium length in mammalian epithelial and mesenchymal cells. Anterograde intraflagellar transport is sped up in lengthened cilia, potentially increasing delivery flux of cilium components. The cilium length response creates a negative feedback loop whereby fluid shear-mediated deflection of the primary cilium, which decreases intracellular cAMP, leads to cilium shortening and thus decreases mechanotransductive signaling. This adaptive response is blocked when the autosomal dominant polycystic kidney disease (ADPKD) gene products, polycystin-1 or -2, are reduced. Dynamic regulation of cilium length is thus intertwined with cilium-mediated signaling and provides a natural braking mechanism in response to external stimuli that may be compromised in PKD.

Background-The Ca 2ϩ -activated chloride channel (CaCC) plays an important role in a variety of physiological functions. In vascular smooth muscle cells, CaCC is involved in the regulation of agonist-stimulated contraction and myogenic tone. The physiological functions of CaCC in blood vessels are not fully revealed because of the lack of specific channel blockers and the uncertainty concerning its molecular identity. Methods and Results-Whole-cell patch-clamp studies showed that knockdown of TMEM16A but not bestrophin-3 attenuated CaCC currents in rat basilar smooth muscle cells. The activity of CaCC in basilar smooth muscle cells isolated from 2-kidney, 2-clip renohypertensive rats was decreased, and CaCC activity was negatively correlated with blood pressure (nϭ25; PϽ0.0001) and medial cross-sectional area (nϭ24; PϽ0

Excluding 53BP1 from chromatin is required to attenuate the DNA damage response during mitosis, yet the functional relevance and regulation of this exclusion is unclear. Here we show that 53BP1 is phosphorylated during mitosis on two residues, T1609 and S1618, located in its well-conserved ubiquitination-dependent recruitment (UDR) motif. Phosphorylating these sites blocks the interaction of the UDR motif with mononuclesomes containing ubiquitinated histone H2A and impedes binding of 53BP1 to mitotic chromatin. Ectopic recruitment of 53BP1- T1609A/S1618A to mitotic DNA lesions was associated with significant mitotic defects that could be reversed by inhibiting non-homologous end joining. We also reveal that protein phosphatase complex, PP4C/R3β dephosphorylates T1609 and S1618 to allow the recruitment of 53BP1 to chromatin in G1 phase. Our results identify key sites of 53BP1 phosphorylation during mitosis, identify the counteracting phosphatase complex that restores the potential for DDR during interphase, and establish the physiological importance of this regulation.