title: Secretory prostate apoptosis response (Par)-4 sensitizes multicellular spheroids (MCS) of glioblastoma multiforme cells to tamoxifen-induced cell death.
abstract: Glioblastoma multiforme (GBM) is the most malignant form of brain tumor and is associated with resistance to conventional therapy and poor patient survival. Prostate apoptosis response (Par)-4, a tumor suppressor, is expressed as both an intracellular and secretory/extracellular protein. Though secretory Par-4 induces apoptosis in cancer cells, its potential in drug-resistant tumors remains to be fully explored. Multicellular spheroids (MCS) of cancer cells often acquire multi-drug resistance and serve as ideal experimental models. We investigated the role of Par-4 in Tamoxifen (TAM)-induced cell death in MCS of human cell lines and primary cultures of GBM tumors. TCGA and REMBRANT data analysis revealed that low levels of Par-4 correlated with low survival period (21.85 ± 19.30 days) in GBM but not in astrocytomas (59.13 ± 47.26 days) and oligodendrogliomas (58.04 ± 59.80 days) suggesting low PAWR expression as a predictive risk factor in GBM. Consistently, MCS of human cell lines and primary cultures displayed low Par-4 expression, high level of chemo-resistance genes and were resistant to TAM-induced cytotoxicity. In monolayer cells, TAM-induced cytotoxicity was associated with enhanced expression of Par-4 and was alleviated by silencing of Par-4 using specific siRNA. TAM effectively induced secretory Par-4 in conditioned medium (CM) of cells cultured as monolayer but not in MCS. Moreover, MCS were rendered sensitive to TAM-induced cell death by exposure to conditioned medium (CM)-containing Par-4 (derived from TAM-treated monolayer cells). Also TAM reduced the expression of Akt and PKCζ in GBM cells cultured as monolayer but not in MCS. Importantly, combination of TAM with inhibitors to PI3K inhibitor (LY294002) or PKCζ resulted in secretion of Par-4 and cell death in MCS. Since membrane GRP78 is overexpressed in most cancer cells but not normal cells, and secretory Par-4 induces apoptosis by binding to membrane GRP78, secretory Par-4 is an attractive candidate for potentially overcoming therapy-resistance not only in malignant glioma but in broad spectrum of cancers.
authors: National Centre for Cell Science (NCCS), Pune, India.
authors: Jayashree C
authors: JC
authors: Jagtap
authors: National Centre for Cell Science (NCCS), Pune, India.
authors: D
authors: D
authors: Parveen
authors: National Centre for Cell Science (NCCS), Pune, India.
authors: Reecha D
authors: RD
authors: Shah
authors: Persistent Systems Ltd., Pune, India.
authors: Aarti
authors: A
authors: Desai
authors: Persistent Systems Ltd., Pune, India.
authors: Dipali
authors: D
authors: Bhosale
authors: Department of Neurosurgery, Cimet's Inamdar Multispeciality Hospital, Pune, India.
authors: Ashish
authors: A
authors: Chugh
authors: Department of Neurosurgery, D.Y. Patil Medical College, Pune, India.
authors: Deepak
authors: D
authors: Ranade
authors: Department of Histopathology, Ruby Hall Clinic, Pune, India.
authors: Swapnil
authors: S
authors: Karnik
authors: Department of Histopathology, Ruby Hall Clinic, Pune, India.
authors: Bhushan
authors: B
authors: Khedkar
authors: National Centre for Cell Science (NCCS), Pune, India.
authors: Aaishwarya
authors: A
authors: Mathur
authors: National Centre for Cell Science (NCCS), Pune, India.
authors: Kumar
authors: K
authors: Natesh
authors: National Centre for Cell Science (NCCS), Pune, India.
authors: Goparaju
authors: G
authors: Chandrika
authors: National Centre for Cell Science (NCCS), Pune, India.
authors: Padma
authors: P
authors: Shastry
keywords: CM, conditioned medium; Cytotoxicity; Drug resistance; GBM, glioblastoma multiforme; Glioblastoma; LGG, low grade gliomas; MCS, multicellular spheroids; Multicellular spheroids (MCS); Par-4; TAM, tamoxifen; TCGA, The Cancer Genome Atlas; Tamoxifen