Enhanced proteasomal activity is essential for long term survival and recurrence of innately radiation resistant residual glioblastoma cells

// Jacinth Rajendra 1, 7 , Keshava K. Datta 2 , Sheikh Burhan Ud Din Farooqee 3, 7 , Rahul Thorat 5 , Kiran Kumar 2 , Nilesh Gardi 4 , Ekjot Kaur 1, 7 , Jyothi Nair 1, 7 , Sameer Salunkhe 1, 7 , Ketaki Patkar 1 , Sanket Desai 4, 7 , Jayant Sastri Goda 8 , Aliasgar Moiyadi 6 , Amit Dutt 4, 7 , Prasanna Venkatraman 3, 7 , Harsha Gowda 2 and Shilpee Dutt 1, 7 1 Shilpee Dutt Laboratory, Tata Memorial Centre, Advanced Centre for Treatment, Research and Education in Cancer (ACTREC), Kharghar, Navi Mumbai, India 2 Institute of Bioinformatics, International Technology Park, Bangalore, India 3 Advanced Centre for Treatment, Research and Education in Cancer (ACTREC), Tata Memorial Centre (TMC), Kharghar, Navi Mumbai, India 4 Integrated Genomics Laboratory, Advanced Centre for Treatment, Research and Education in Cancer, Tata Memorial Centre, Navi Mumbai, Maharashtra, India 5 Laboratory Animal Facility, Advanced Centre for Treatment, Research and Education in Cancer (ACTREC), Tata Memorial Centre (TMC), Kharghar, Navi Mumbai, India 6 Department of neurosurgery Tata Memorial Centre, Advanced Centre for Treatment, Research and Education in Cancer, Navi Mumbai, India 7 Homi Bhabha National Institute, Training School Complex, Anushakti Nagar, Mumbai, India 8 Department of Radiation Oncology, Tata Memorial Centre, Advanced Centre for Treatment, Research and Education in Cancer, Navi Mumbai, India Correspondence to: Shilpee Dutt, email: sdutt@actrec.gov.in Keywords: glioblastoma; radio-resistant cells; recurrence; proteomic analysis; proteasomes Received: August 28, 2017      Accepted: April 25, 2018      Published: June 12, 2018 ABSTRACT Therapy resistance and recurrence in Glioblastoma is due to the presence of residual radiation resistant cells. However, because of their inaccessibility from patient biopsies, the molecular mechanisms driving their survival remain unexplored. Residual Radiation Resistant (RR) and Relapse (R) cells were captured using cellular radiation resistant model generated from patient derived primary cultures and cell lines. iTRAQ based quantitative proteomics was performed to identify pathways unique to RR cells followed by in vitro and in vivo experiments showing their role in radio-resistance. 2720 proteins were identified across Parent (P), RR and R population with 824 and 874 differential proteins in RR and R cells. Unsupervised clustering showed proteasome pathway as the most significantly deregulated pathway in RR cells. Concordantly, the RR cells displayed enhanced expression and activity of proteasome subunits, which triggered NFkB signalling. Pharmacological inhibition of proteasome activity led to impeded NFkB transcriptional activity, radio-sensitization of RR cells in vitro , and significantly reduced capacity to form orthotopic tumours in vivo . We demonstrate that combination of proteasome inhibitor with radio-therapy abolish the inaccessible residual resistant cells thereby preventing GBM recurrence. Furthermore, we identified first proteomic signature of RR cells that can be exploited for GBM therapeutics.