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The tyrosine kinase receptor ROR1 is constitutively phosphorylated in chronic lymphocytic leukemia (CLL) cells.

ABSTRACT: Phosphorylation of receptor tyrosine kinases (RTKs) has a key role in cellular functions contributing to the malignant phenotype of tumor cells. We and others have previously demonstrated that RTK ROR1 is overexpressed in chronic lymphocytic leukemia (CLL). Silencing siRNA downregulated ROR1 and induced apoptosis of CLL cells. In the present study we analysed ROR1 isoforms and the phosphorylation pattern in CLL cells (n=38) applying western blot and flow-cytometry using anti-ROR1 antibodies and an anti-phospho-ROR1 antibody against the TK domain. Two major ROR1 bands with the size of 105 and 130 kDa respectively were identified, presumably representing unglycosylated (immature) and glycosylated (mature) ROR1 respectively as well as a 260 kDa band which may represent dimerized ROR1. A ROR1 band of 64 kDa that may correspond to a C-terminal fragment was also noted, present only in the nucleus. The 105 kDa ROR1 isoform was more frequently expressed in non-progressive as compared to progressive CLL patients (p=0.03). The 64, 105, 130 and 260 kDa bands were constitutively phosphorylated both at tyrosine and serine residues. Phosphorylation intensity of the mature (130 kDa) isoform was significantly higher in progressive than in non-progressive disease (p<0.001). Incubation of CLL cells with a mouse anti-ROR1 KNG or an anti-ROR1 CRD mAb respectively induced dephosphorylation of ROR1 before entering apoptosis. In conclusion CLL cells expressed different isoforms of ROR1 which were constitutively phosphorylated. The mature, phosphorylated ROR1 isoform was associated with a progressive disease stage. Targeting ROR1 by mAbs induced specific dephosphorylation and leukemic cell death. ROR1 might be an interesting therapeutic target.

SUBMITTER: Hojjat-Farsangi M

PROVIDER: S-EPMC3813472 | biostudies-literature | 2013

REPOSITORIES: biostudies-literature

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The tyrosine kinase receptor ROR1 is constitutively phosphorylated in chronic lymphocytic leukemia (CLL) cells.

Hojjat-Farsangi Mohammad M Khan Abdul Salam AS Daneshmanesh Amir Hossein AH Moshfegh Ali A Sandin Asa A Mansouri Ladan L Palma Marzia M Lundin Jeanette J Österborg Anders A Mellstedt Håkan H

PloS one 20131024 10

Phosphorylation of receptor tyrosine kinases (RTKs) has a key role in cellular functions contributing to the malignant phenotype of tumor cells. We and others have previously demonstrated that RTK ROR1 is overexpressed in chronic lymphocytic leukemia (CLL). Silencing siRNA downregulated ROR1 and induced apoptosis of CLL cells. In the present study we analysed ROR1 isoforms and the phosphorylation pattern in CLL cells (n=38) applying western blot and flow-cytometry using anti-ROR1 antibodies and ...[more]

PMID: 24205204

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Project description:Purpose of reviewThere have been significant advances in the treatment of relapsed/refractory chronic lymphocytic leukemia (CLL) over the past two decades. However, the intention of treatment remains control of the disease and delay of progression rather than a cure which remains largely elusive. Considering that CLL is mostly seen in older patients, there are multiple factors that play a role in the selection of CLL beyond the frontline treatment. Here, we review the concept of relapsed CLL, factors that predispose to relapse, and therapeutic options available to this patient population. We also review investigational therapies and provide a framework for selection of therapies in this setting.Recent findingsPlease check if the affiliations are presented correctly.Targeted therapies with continuous BTK inhibitors (BTKi) or fixed duration venetoclax plus anti-CD20 monoclonal antibody therapy have established superiority over chemoimmunotherapy in relapsed CLL and have become the preferred standard of care treatment. The second-generation more selective BTK inhibitors (acalabrutinib and zanubrutinib) have shown improved safety profile compared to ibrutinib. However, resistance to the covalent BTK inhibitors may emerge and is commonly associated with mutations in BTK or other downstream enzymes. The novel non-covalent BTK inhibitors such as pirtobrutinib (Loxo-305) and nemtabrutinib (ARQ 531) are showing promising activities for relapsed CLL refractory to prior covalent BTKi. Other novel therapies such as chimeric antigen receptor (CAR) T cell therapy have also shown significant activities for relapsed and refractory CLL. Measurable residual disease (MRD) assessment has a growing importance in venetoclax-based limited-duration therapy and there is mounting evidence that MRD negativity improves outcomes. However, it remains to be seen if this will become an established clinically significant endpoint. Further, the optimal sequence of various treatment options remains to be determined. Patients with relapsed CLL now have more options for the treatment of the disease. The choice of therapy is best individualized especially in the absence of direct comparisons of targeted therapies, and the coming years will bring more data on the best sequence of use of the therapeutic agents.

Dataset Information

The tyrosine kinase receptor ROR1 is constitutively phosphorylated in chronic lymphocytic leukemia (CLL) cells.

Publications

The tyrosine kinase receptor ROR1 is constitutively phosphorylated in chronic lymphocytic leukemia (CLL) cells.

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