SQSTM1-NTRK1, a kinase gets fused with a garbage disposal protein

The SQSTM1 gene product, p62, is a scaffold protein involved in protein turnover and signaling. p62 is commonly found in dense protein bodies in eukaryotic cells. In autophagy, p62 (the protein) shuttles ubiquitnated proteins to the autophagosome for degradation (Ciuffa 2015). What will become apparent in this discussion is that the wildtype protein products of the SQSTM1 and NTRK1 genes, p62 and TrkA, are signaling partners in the cell.

Estimated protein expression of p62 in various tissues and cells.

p62 tissue expression.

Though p62 is known for its association with diseases of the nervous system, it’s expression on the protein level is pretty ubiquitous.

 

Diseases caused by variations in the SQSTM1 gene

(genecards unless otherwise noted)

  • Paget Disease of the Bone 3.
  • Frontotemporal Dementia and/or Amyotrophic Lateral Sclerosis 3.
  • Alzheimer’s Disease (Zheng, 2015).
  • May also contribute to cancer progression (Moscat and Diaz-Meco, 2014).

 

Functions p62, the SQSTM1  gene product

(UniProt unless otherwise noted)

  • Interacts with damaged/misfolded protein destined for degradation (autophagy).
  • Modifies microtubule associated protein 1 (MAP1) and light chain 3 (LC3).
  • Required both for the formation and autophagic degradation of polyubiquitin-containing bodies, called ALIS (aggresome-like induced structures).
  • Links ALIS to the autophagic machinery.
  • May regulate the activation of NFKb1 by TNFa, NGF, and interleukin-1.
  • May play a role in titin/TTN downstream signaling in muscle cells.
  • May regulate signaling cascades through ubiquitination.
  • Adapter that mediates the interaction between TRAF6 and CYLD (By similarity).
  • May be involved in cell differentiation, apoptosis, immune response, and regulation of K+.
  • Binds to and functions as a scaffold protein with tropomyosin kinases and downstream targets (Wooten, 2001, Geetha, 2003, Geetha, 2005).
Estimated p62 protein expression in various human tissues and cells.

p62 expression.

Note that p62 is expressed in a variety of tissues.

SQSTM1 and NTRK1 the genes

Note the presence of the SQSTM1 gene at the tip of the long arm of chromosome 5.

Ensembl chromosome 5 and 1 showing SQSTM1and NTRK1 gene location respectively.

The chromosome location of the SQSTM1 and NTRK1 genes, Genecards.

p62 and TrkA the proteins

Protein domains for p62 come from UniProt or were created in the same style from the references below. In no way is this list complete. The approximate position of exons in relation to three domains is also shown.

Picture showing p62 and TrkA proetion domains. Inset shows SQSTM1-NTRK1 fusion gene with exons.

Protein domains of p62 (SQSTM1 gene) and TrkA (NTRK gene).

p62 is a scaffold protein for TrkA signaling

Geetha (2002) began their study with the observation that internalized TrkA receptors continue to signal within the endosomal compartment and are required to mediate NGF-induced differentiation.  The observation that inhibition of p62 expression inhibits neurite outgrowth also influenced the study (Geetha, 2002). Blocking p62 protein expression with anti-sense RNA also blocked the NGF stimulated intracellular localization of activated TrkA along with p62 in an endosomal compartment (Geetha, 2002).  One could imagine the effective concentration of NGF in the endosome being at least in the mM range.

 

Cartoon showing p62 relation to NGF in endocytosis process along with signal cascades showing various other factors interacting in membrane.

Some views of p62 as it relates to NGF from the literature  A.  When nerve growth factor (NGF) binds to TrkA, p62 is recruited to the kinase side to promote receptor endocytosis.  B.  Binding of NGF to the lower affinity receptor p75 links p75 to TrkA via Traf6.  The cytoplasmic (kinase side) of TrkA also gets labeled with ubiquitin.  C.  When NGF is not cleaved from the pro-peptide to its active form, neurons die.

Zheng and coworkers (2016) studied the relationship between Trk and neuronal survival in Alzheimer’s Disease (AD) with unanticipated results.

  1. ProNGF, the precursor form of NGF, is cleaved by the matrix metalloproteinase-7 (mmp7). They found mmp7 decreased in AD patients’ brains.
  2. TrkA activation leads to activation of Ras/MAPK, PI3K/Akt pathways, and so on.  In neurons, this leads to interception of  nuclear and mitochondrial cell death programs, i.e. survival.
  3. The Alzheimers Aβ peptide prevented NGF induced autophosphorylation of Tyr99, ubiquitination of TrkA, association with TRAF6, p62 and p75NTR.
  4. All of these events were correlated with decreased phosphorylation of down stream effectors in both the PC12 cells and in the brains of AD patients.

These results have interesting implications in p62 – TrkA cancers that might be accompanied by oxidative and nitrosative stress.

The PB1 domain

Fig A shows comparison of p62-TrkA fusion protein domains in relation to other similar domain proteins. Fig B shows region of p62 where amino acids bind to TrkA. Fig C shows dimers and polymers of p62 interaction with TrkA.

The PB1 domain in kinases and oligomers   A. This image was adapted from a Moscat, 2006 review proposing how the p62-TrA fusion protein might fit into the natural scheme of PB1 domain fusion proteins. B.  A region between amino acids 101 and 122 plays a role in polymerization.  There is additional structure between 122 and the start of the Trk fusion protein.    If there are no steric constraints, the kinase domains of Trk may be close enough for auto phosphorylation.  C.  After dimers form, multimers form.   In absence of other proteins, the PB1 domains organize themselves into filaments.  PB1 of p62 domain images are from Ciuffa,  2015.

Important information:

Our investigation of the SQSTM1NTRK1 was inspired by a report (Farago, 2015) demonstrating tumor reduction with entrictinib in  a non small cell lung cancer (NSCLC) patient with with central nervous system metastases. Upon reviewing the literature, we have a greater understanding of the success of Entrectinib in this particular fusion mutation.

For solid tumor patients with SQSTMQNTRK1 mutations as well as other kinase (ROS1, ALK, NTRK1, NTRK2, NTRK3) fusion mutations, there is an open NTRK fusion clinical trial, that is actively enrolling  patients (STARTRK-2), with more information on the NTRK trial website.

References:

Ciuffa R, Lamark T, Tarafder AK, Guesdon A, Rybina S, Hagen WJ, Johansen T, Sachse C. (2015) The selective autophagy receptor p62 forms a flexible filamentous helical scaffold. Cell Rep. 11(5):748-58.  PubMed

Farago AF, Le LP, Zheng Z, Muzikansky A, Drilon A, Patel M, Bauer TM, Liu SV, Ou SH, Jackman D, Costa DB, Multani PS, Li GG, Hornby Z, Chow-Maneval E, Luo D, Lim JE, Iafrate AJ, Shaw AT (2015) Durable Clinical Response to Entrectinib in NTRK1-Rearranged Non-Small Cell Lung Cancer. J Thorac Oncol.10(12):1670-4.  PubMed

Geetha T, Wooten MW (February 2003) Association of the atypical protein kinase C-interacting protein p62/ZIP with nerve growth factor receptor TrkA regulates receptor trafficking and Erk5 signaling. J. Biol. Chem278 (7): 4730–9. PubMed

Geetha T, Jiang J, Wooten MW. (2005) Lysine 63 polyubiquitination of the nerve growth factor receptor TrkA directs internalization and signaling. Mol Cell. 20(2):301-12. PubMed

Moscat J, Diaz-Meco MT, Albert A, Campuzano S. (2006) Cell signaling and function organized by PB1 domain interactions. Mol Cell. 23(5):631-40. Review.  PubMed

Moscat J, Diaz-Meco MT.(2009) p62 at the crossroads of autophagy, apoptosis, and cancer. Cell.137(6):1001-4.  PubMed

Wooten MW, Seibenhener ML, Mamidipudi V, Diaz-Meco MT, Barker PA, Moscat J (2001) The atypical protein kinase C-interacting protein p62 is a scaffold for NF-kappaB activation by nerve growth factor. J. Biol. Chem276 (11): 7709–12. PubMed

Zheng C, Geetha T, Gearing M, Babu JR. (2015) Amyloid β-abrogated TrkA ubiquitination in PC12 cells analogous to Alzheimer’s disease.  J Neurochem. 133(6):919-25.  PubMed

 

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