Genetic inactivation of p62 leads to accumulation of hyperphosphorylated tau and neurodegeneration

The signaling adapter p62 plays a coordinating role in mediating phosphorylation and ubiquitin-dependent trafficking of interacting proteins. However, there is little known about the physiologic role of this protein in brain. Here, we report age-dependent constitutive activation of glycogen synthase kinase 3β, protein kinase B, mitogen-activated protein kinase, and c- Jun -N-terminal kinase in adult p62^−/− mice resulting in hyperphosphorylated tau, neurofibrillary tangles, and neurodegeneration. Biochemical fractionation of p62^−/− brain led to recovery of aggregated K63-ubiquitinated tau. Loss of p62 was manifested by increased anxiety, depression, loss of working memory, and reduced serum brain-derived neurotrophic factor levels. Our findings reveal a novel role for p62 as a chaperone that regulates tau solubility thereby preventing tau aggregation. This study provides a clear demonstration of an Alzheimer-like phenotype in a mouse model in the absence of expression of human genes carrying mutations in amyloid-beta protein precursor, presenilin, or tau. Thus, these findings provide new insight into manifestation of sporadic Alzheimer disease and the impact of obesity.     

Protein Kinase C�� Mediates Cigarette Smoke/Aldehyde- and Lipopolysaccharide-induced Lung Inflammation and Histone Modifications

Atypical protein kinase C (PKC) ζ is an important regulator of inflammation through activation of the nuclear factor-κB (NF-κB) pathway. Chromatin remodeling on pro-inflammatory genes plays a pivotal role in cigarette smoke (CS)- and lipopolysaccharide (LPS)-induced abnormal lung inflammation. However, the signaling mechanism whereby chromatin remodeling occurs in CS- and LPS-induced lung inflammation is not known. We hypothesized that PKCζ is an important regulator of chromatin remodeling, and down-regulation of PKCζ ameliorates lung inflammation by CS and LPS exposures. We determined the role and molecular mechanism of PKCζ in abnormal lung inflammatory response to CS and LPS exposures in PKCζ-deficient (PKCζ^−/−) and wild-type mice. Lung inflammatory response was decreased in PKCζ^−/− mice compared with WT mice exposed to CS and LPS. Moreover, inhibition of PKCζ by a specific pharmacological PKCζ inhibitor attenuated CS extract-, reactive aldehydes (present in CS)-, and LPS-mediated pro-inflammatory mediator release from macrophages. The mechanism underlying these findings is associated with decreased RelA/p65 phosphorylation (Ser³¹¹) and translocation of the RelA/p65 subunit of NF-κB into the nucleus. Furthermore, CS/reactive aldehydes and LPS exposures led to activation and translocation of PKCζ into the nucleus where it forms a complex with CREB-binding protein (CBP) and acetylated RelA/p65 causing histone phosphorylation and acetylation on promoters of pro-inflammatory genes. Taken together, these data suggest that PKCζ plays an important role in CS/aldehyde- and LPS-induced lung inflammation through acetylation of RelA/p65 and histone modifications via CBP. These data provide new insights into the molecular mechanisms underlying the pathogenesis of chronic inflammatory lung diseases.     

The atypical PKC-interacting protein p62 is an important mediator of RANK-activated osteoclastogenesis

The atypical PKCs (aPKCs) have been implicated genetically in at least two independent signaling cascades that control NF-kappa B and cell polarity, through the interaction with the adapters p62 and Par-6, respectively. P62 binds TRAF6, which plays an essential role in osteoclastogenesis and bone remodeling. Recently, p62 mutations have been shown to be the cause of the 5q35-linked Paget's disease of bone, a genetic disorder characterized by aberrant osteoclastic activity. Here we show that p62, like TRAF6, is upregulated during RANK-L-induced osteoclastogenesis and that the genetic inactivation of p62 in mice leads to impaired osteoclastogenesis in vitro and in vivo, as well as inhibition of IKK activation and NF-kappa B nuclear translocation. In addition, RANK-L stimulation leads to the inducible formation of a ternary complex involving TRAF6, p62, and the aPKCs. These observations demonstrate that p62 is an important mediator during osteoclastogenesis and induced bone remodeling.     

Cigarette smoke-induced accumulation of lung dendritic cells is interleukin-1α-dependent in mice

Background

Evidence suggests that dendritic cells accumulate in the lungs of COPD patients and correlate with disease severity. We investigated the importance of IL-1R1 and its ligands IL-1α and β to dendritic cell accumulation and maturation in response to cigarette smoke exposure.

Methods

Mice were exposed to cigarette smoke using a whole body smoke exposure system. IL-1R1-, TLR4-, and IL-1α-deficient mice, as well as anti-IL-1α and anti-IL-1β blocking antibodies were used to study the importance of IL-1R1 and TLR4 to dendritic cell accumulation and activation.

Results

Acute and chronic cigarette smoke exposure led to increased frequency of lung dendritic cells. Accumulation and activation of dendritic cells was IL-1R1/IL-1α dependent, but TLR4- and IL-1β-independent. Corroborating the cellular data, expression of CCL20, a potent dendritic cells chemoattractant, was IL-1R1/IL-1α-dependent. Studies using IL-1R1 bone marrow-chimeric mice revealed the importance of IL-1R1 signaling on lung structural cells for CCL20 expression. Consistent with the importance of dendritic cells in T cell activation, we observed decreased CD4⁺ and CD8⁺ T cell activation in cigarette smoke-exposed IL-1R1-deficient mice.

Conclusion

Our findings convey the importance of IL-1R1/IL-1α to the recruitment and activation of dendritic cells in response to cigarette smoke exposure.     

Cell signaling and function organized by PB1 domain interactions

The PB1-domain-containing proteins p62, aPKC, MEKK2/MEKK3, MEK5, and Par-6 play roles in critical cell processes like osteoclastogenesis, angiogenesis, and early cardiovascular development or cell polarity. PB1 domains are scaffold modules that adopt the topology of ubiquitin-like beta-grasp folds that interact with each other in a front-to-back mode to arrange heterodimers or homo-oligomers. The different PB1 domain adaptors provide specificity for PB1 kinases to ensure the effective transmission of cellular signals. Also, recent data suggest that PB1 domains may serve to orchestrate signaling cascades not involving other PB1 domains, such as the MEK5-ERK5 and p62-ERK1 interactions.     

zeta PKC induces phosphorylation and inactivation of I kappa B-alpha in vitro.

The zeta isotype of protein kinase C (zeta PKC), a distinct PKC unable to bind phorbol esters, is required during NF-kappa B activation as well as in mitogenic signalling in Xenopus oocytes and mammalian cells. To investigate the mechanism(s) for control of cellular functions by zeta PKC, this enzyme was expressed in Escherichia coli as a fusion protein with maltose binding protein (MBP), to allow immobilization on amylose beads to study signalling proteins in cell extracts that might form complex(es) with zeta PKC. The following evidence for interaction with the NF-kappa B/I kappa B pathway was obtained. MBP-zeta PKC, but not MBP, bound and activated a potentially novel I kappa B kinase of approximately 50 kDa molecular weight able to regulate I kappa B-alpha function. Activation of the I kappa B kinase was dependent on zeta PKC enzymatic activity and ATP, suggesting that zeta PKC controls, directly or indirectly, the activity of a functionally significant I kappa B kinase. Importantly, zeta PKC immunoprecipitates from TNF-alpha-stimulated NIH-3T3 fibroblasts displayed a higher I kappa B phosphorylating activity than untreated controls, indicating the in vivo relevance of these findings. We also show here that zeta PKC associates with and activates MKK-MAPK in vitro, suggesting that one of the mechanisms whereby overexpression of zeta PKC leads to deregulation of cell growth may be accounted for at least in part by activation of the MKK-MAPK complex. However, neither MKK nor MAPK is responsible for the putative I kappa B phosphorylating activity. These data provide a decisive step towards understanding the functions of zeta PKC.     

Stromal SOX2 Upregulation Promotes Tumorigenesis through the Generation of a SFRP1/2-Expressing Cancer-Associated Fibroblast Population

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