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Endomembrane flow is a physiological process that leads to maturation of organelles such as endosomes and lysosomes and influences the composition of the plasma membrane.

This maturation process is highly dynamic and is volatile for abnormalities in its sorting system, acidification and protein composition. It is a key regulator of proteostasis by balancing cellular protein degradation and recycling. A challenge is to understand the molecular mechanisms and interconnectivity of the events that changes the function of the endosome-lysosome-autophagy pathway and leads to disease such as neurological disorders and cancers.

We have developed microscopy and live cell-based protein trafficking and protein-protein assays to monitor the dynamic nature of endosomal flow and lysosome-autophagy function. Components and identified protein networks from screenings are tested in experimental systems. We have connected the events of pH regulation, ubiquitination and ubiquitin-dependent protein complexes of ESCRTs (endosomal sorting complexes for transport) and signalling to the kinetics of vesicle movement, and to surveillance machinery of protein quality control.

Our goal is to gain insights into the relationship between signalling and changes in protein trafficking and organelle function. Our second major interest is in the biology of ionic regulation in organelle function.

We are particularly interested in connecting proteostasis regulation to the cellular-signalling cascades and functionality of the endolysomal-autophagy pathway system. Combining single-cell fluorescence image analyses to biosensors and to specific membrane cargoes provides us a way to dissect spatially how vesicle/organelle movement is connected to signalling.

We will continue to use our ubiquitination assays, protein-protein interaction analyses and constructed networks to determine the specific trafficking pathways.

In addition, we are further investigating the membrane-sensing in organelle volume regulation. From screenings, we have identified new candidate proteins for our investigations into how activity and dynamics of membrane trafficking are orchestrated.

A/Prof Pirjo Apaja was an EMBL Australia Group Leader in the South Australian Node, based in the Nutrition and Metabolism Theme, Lysosomal Diseases Research Unit at the South Australian Health and Medical Research Institute. 

After completing a PhD concerning processing and trafficking of G protein-coupled receptors during development in University of Oulu, Finland, she continued her research work into function of ubiquitin-mediated membrane trafficking at the Hospital for Sick Children Research Institute, Toronto and McGill University, Montreal, Canada. 

She has made seminal discoveries including the role of ubiquitin ligases in conformation disposal of misfolded membrane proteins, and the role of endosomal pH and ESCRT-complexes in cancers. Dr Apaja’s research focuses on membrane trafficking and, in particular, the functional crosstalk between signalling and pH on endo-lysosome-autophagy regulation. Her group investigated the role of this system in astrocyte volume regulation and in GPCR variant signalling.

In 2016, she joined EMBL Australia. Her laboratory combined experimental systems using targeted proteomics, advanced light microscopy on single-molecule fluorescence-based subcellular trafficking, FRET for signalling complexes using biosensors, biochemical assays and genome editing. 

View A/Prof Pirjo Apaja's ORCID profile.

Highlight publications

Published In

Hein LK, Apaja PM, Hattersley K, Grose RH, Xie J, Proud CG, Sargeant TJ.

A novel fluorescent probe reveals starvation controls the commitment of amyloid precursor protein to the lysosome.

Biochim Biophys Acta. 2017 Oct;1864(10):1554-1565. doi: 10.1016/j.bbamcr.2017.06.011. Epub 2017 Jun 19. PMID: 28641977

Gaitán-Peñas H, Apaja PM, Arnedo T, Castellanos A, Elorza-Vidal X, Soto D, Gasull X, Lukacs GL, Estévez R.

Leukoencephalopathy-causing CLCN2 mutations are associated with impaired Cl- channel function and trafficking.

J Physiol. 2017 Sep 14. doi: 10.1113/JP275087

Bagdany M, Veit G, Fukuda R, Avramescu RG, Okiyoneda T, Baaklini I, Singh J, Sovak G, Xu H, Apaja PM, Sattin S, Beitel LK, Roldan A, Colombo G, Balch W, Young JC, Lukacs GL.

Chaperones rescue the energetic landscape of mutant CFTR at single molecule and in cell.

Nat Commun. 2017 Aug 30;8(1):398. doi: 10.1038/s41467-017-00444-4.

Kharitidi D, Apaja PM, Manteghi S, Suzuki K, Malitskaya E, Roldan A, Gingras MC, Takagi J, Lukacs GL, Pause A.

Interplay of endosomal pH and ligand occupancy in integrin 51 ubiquitination, endocytic sorting and cell migration.

Cell Rep. 2015 Oct 20;13(3):599-609. doi: 10.1016/j.celrep.2015.09.024. Epub 2015 Oct 8.

Apaja PM and Lukacs GL.

Protein homeostasis at the plasma membrane.

Physiology (Bethesda). 2014 Jul;29(4):265–277. doi: 10.1152/physiol.00058.2013.

Veit G, Avramescu RG, Perdomo D, Phuan PW, Bagdany M, Apaja PM, Borot F, Szollosi D, Wu YS, Finkbeiner WE, Hegedus T, Verkman AS, Lukacs GL.

Some gating potentiators, including VX-770, diminish ΔF508-CFTR functional expression.

Sci Transl Med. 2014 Jul 23;6(246):246ra97. doi: 10.1126/scitranslmed.3008889.

Chu CY, King J, Berrini M, Rumley AC, Apaja PM, Lukacs GL, Alexander RT, Cordat E.

Degradation mechanism of a Golgi-retained distal renal tubular acidosis mutant of the kidney anion exchanger 1 in renal cells.

Am J Physiol Cell Physiol. 2014 Aug 1;307(3):C296-307. doi: 10.1152/ajpcell.00310.2013. Epub 2014 Jun 11.

Okiyoneda T, Apaja PM and Lukacs GL.

Protein quality control at the plasma membrane.

Curr Opin Cell Biol. 2011 Aug;23(4):483-91. doi: 10.1016/ Epub 2011 May 14.