Phosphoproteomic screening identifies Rab GTPases as novel downstream targets of PINK1

Mutations in the PTEN‐induced kinase 1 (PINK1) are causative of autosomal recessive Parkinson''s disease (PD). We have previously reported that PINK1 is activated by mitochondrial depolarisation and phosphorylates serine 65 (Ser⁶⁵) of the ubiquitin ligase Parkin and ubiquitin to stimulate Parkin E3 ligase activity. Here, we have employed quantitative phosphoproteomics to search for novel PINK1‐dependent phosphorylation targets in HEK (human embryonic kidney) 293 cells stimulated by mitochondrial depolarisation. This led to the identification of 14,213 phosphosites from 4,499 gene products. Whilst most phosphosites were unaffected, we strikingly observed three members of a sub‐family of Rab GTPases namely Rab8A, 8B and 13 that are all phosphorylated at the highly conserved residue of serine 111 (Ser¹¹¹) in response to PINK1 activation. Using phospho‐specific antibodies raised against Ser¹¹¹ of each of the Rabs, we demonstrate that Rab Ser¹¹¹ phosphorylation occurs specifically in response to PINK1 activation and is abolished in HeLa PINK1 knockout cells and mutant PINK1 PD patient‐derived fibroblasts stimulated by mitochondrial depolarisation. We provide evidence that Rab8A GTPase Ser¹¹¹ phosphorylation is not directly regulated by PINK1 in vitro and demonstrate in cells the time course of Ser¹¹¹ phosphorylation of Rab8A, 8B and 13 is markedly delayed compared to phosphorylation of Parkin at Ser⁶⁵. We further show mechanistically that phosphorylation at Ser¹¹¹ significantly impairs Rab8A activation by its cognate guanine nucleotide exchange factor (GEF), Rabin8 (by using the Ser111Glu phosphorylation mimic). These findings provide the first evidence that PINK1 is able to regulate the phosphorylation of Rab GTPases and indicate that monitoring phosphorylation of Rab8A/8B/13 at Ser¹¹¹ may represent novel biomarkers of PINK1 activity in vivo. Our findings also suggest that disruption of Rab GTPase‐mediated signalling may represent a major mechanism in the neurodegenerative cascade of Parkinson''s disease.     

Biomarkers: in combination they may do better

The field of biomarkers is a growing one, particularly in osteoarthritis (OA). OA is the most common disabling condition in older persons and a major cause of morbidity. While the debate continues about which of the involved tissues - cartilage, bone or synovium - is the most important in OA aetiology, there is no doubt that the three develop abnormalities in concert; perhaps a truly useful biomarker will reflect just that. While efforts continue to identify reliable biomarkers useful for characterising the status, prognosis and measurement of treatment response in OA, combining existing biomarkers to improve their accuracy looks promising.     

Determination of acid α-naphthyl acetate esterase enzyme activity in peripheral blood leukocytes of gazelles (Gazella subgutturosa)

We examined gazelle peripheral blood leucocytes using the α-Naphthyl acetate esterase (ANAE) staining technique (pH 5.8). Our purpose was to determine the percentage of ANAE positive lymphocytes. The proportion of ANAE positive T-lymphocytes was 72%. T-lymphocytes showed an ANAE positive reaction, but eosinophilic granulocytes and monocytes also showed a positive reaction. By contrast, no reaction was detected in B-lymphocytes, neutrophil granulocytes or platelets. The reaction observed in T-lymphocytes was a red-brown coloration, usually 1–2 granules, but enough granules to fill the cytoplasm were detected rarely. As a result of ANAE enzyme staining, we concluded that the staining technique can be used as a cytochemical marker for gazelle T-lymphocytes.     

Airway cellularity, lipid laden macrophages and microbiology of gastric juice and airways in children with reflux oesophagitis

Background and methods

Human metapneumovirus (hMPV) is a recently discovered respiratory virus associated with bronchiolitis, pneumonia, croup and exacerbations of asthma. Since respiratory viruses are frequently detected in patients with acute exacerbations of COPD (AE-COPD) it was our aim to investigate the frequency of hMPV detection in a prospective cohort of hospitalized patients with AE-COPD compared to patients with stable COPD and to smokers without by means of quantitative real-time RT-PCR.

Results

We analysed nasal lavage and induced sputum of 130 patients with AE-COPD, 65 patients with stable COPD and 34 smokers without COPD. HMPV was detected in 3/130 (2.3%) AE-COPD patients with a mean of 6.5 × 10⁵ viral copies/ml in nasal lavage and 1.88 × 10⁵ viral copies/ml in induced sputum. It was not found in patients with stable COPD or smokers without COPD.

Conclusion

HMPV is only found in a very small number of patients with AE-COPD. However it should be considered as a further possible viral trigger of AE-COPD because asymptomatic carriage is unlikely.     

Colonization factors of diarrheagenicE. coli and their intestinal receptors

WhileEscherichia coli is common as a commensal organism in the distal ileum and colon, the presence of colonization factors (CF) on pathogenic strains ofE. coli facilitates attachment of the organism to intestinal receptor molecules in a species- and tissue-specific fashion. After the initial adherence, colonization occurs, and the involvement of additional virulence determinants leads to illness. EnterotoxigenicE. coli (ETEC) is the most extensively studied of the five categories ofE. coli that cause diarrheal disease, and has the greatest impact on health worldwide. ETEC can be isolated from domestic animals and humans. The biochemistry, genetics, epidemiology, antigenic characteristics, and cell and receptor binding properties of ETEC have been extensively described. Another major category, enteropathogenicE. coli (EPEC), has virulence mechanisms, primarily effacement and cytoskeletal rearrangement of intestinal brush borders, that are distinct from ETEC. An EPEC CF receptor has been purified and characterized as a sialidated transmembrane glycoprotein complex directly attached to actin, thereby associating CF-binding with host-cell response. Three, additional categories ofE. coli diarrheal disease, their colonization factors and their host cell receptors are discussed. It appears that biofilms exist in the intestine in a manner similar to oral bacterial biofilms, and thatE. coli is part of these biofilms as both commensals and pathogens.Abbreviations CF colonization factor - CFA Colonization Factor Antigen - CS coli-surface-associated antigen - EAggEC enteroaggregativeE. coli - ECDD E. coli diarrheal disease - EHEC enterohemorrhagicE. coli - EIEC enteroinvasiveE. coli - EPEC enteropathogenicE. coli - ETEC enterotoxigenicE. coli - Gal galactose - GalNAc N-acetyl galactosamine - LT heat-labile toxin - NeuAc N-acetyl neuraminic acid - PCF Putative colonization factor - RBC red blood cells - SLT Shiga-like toxin - ST heat-stable toxin