Calreticulin (CALR) +1 frameshift mutations in exon 9 are prevalent in myeloproliferative neoplasms. Mutant CALRs possess a new C-terminal sequence rich in positively charged amino acids, leading to activation of the thrombopoietin receptor (TpoR/MPL). We show that the new sequence endows the mutant CALR with rogue chaperone activity, stabilizing a dimeric state and transporting TpoR and mutants thereof to the cell surface in states that would not pass quality control; this function is absolutely required for oncogenic transformation. Mutant CALRs determine traffic via the secretory pathway of partially immature TpoR, as they protect N117-linked glycans from further processing in the Golgi apparatus. A number of engineered or disease-associated TpoRs such as TpoR/MPL R102P, which causes congenital thrombocytopenia, are rescued for traffic and function by mutant CALRs, which can also overcome endoplasmic reticulum retention signals on TpoR. In addition to requiring N-glycosylation of TpoR, mutant CALRs require a hydrophobic patch located in the extracellular domain of TpoR to induce TpoR thermal stability and initial intracellular activation, whereas full activation requires cell surface localization of TpoR. Thus, mutant CALRs are rogue chaperones for TpoR and traffic-defective TpoR mutants, a function required for the oncogenic effects.

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Cell division is the foundation to development and the regulation of cell cycle progression is therefore of paramount importance to the living organisms. Primary control of cell cycle is achieved by an array of cyclins and cyclin dependent kinases (CDKs). The functions of these cyclin-CDK complexes are again regulated by a host of cyclin dependent kinase inhibitors (CDKI). Till date CDKIs are broadly classified into two groups-INK4 family (p15, p16, p18, and p19) and the cip/kip family (p21, p27, and p57). Collectively these CDKIs regulate the progression from G1 to S phase of cell cycle. This review summarizes the functions of p27 while highlighting its emerging roles in leukemia.

TP53 also known as p53 is a tumor suppressor gene mutated in a variety of cancers. P53 is involved in cell cycle, apoptosis and DNA repair mechanisms and is thus tightly controlled by many regulators. Recently, strategies to treat cancer have focused on the development of MDM2 antagonists to induce p53 stabilization and restore cell death in p53 non-mutated cancers. However, some of these molecules display adverse effects in patients including induction of thrombocytopenia. In the present study, we have explored the effect of SAR405838 not only on human megakaryopoiesis but also more generally on hematopoiesis. We compared its effect to MI-219 and Nutlin, which are less potent MDM2 antagonists than SAR405838. We found that all these compounds induce a deleterious effect on all types of hematopoietic progenitors, as well as on erythroid and megakaryocytic differentiation. Moreover, they inhibit both early and late stages of megakaryopoiesis including ploidization and proplatelet formation. In conclusion, MDM2 antagonists induced a major hematopoietic defect in vitro as well as an inhibition of all stages of megakaryopoiesis that may account for in vivo thrombocytopenia observed in treated patients.

Lupeol is a triterpenoid, present in most of the medicinally effective plants and possess a wide range of biological activity against human diseases. The present study aims at evaluating the anticancer potentials of lupeol, isolated from the leaves of Elephantopus scaber L. and thereby explores its action on key cancer marker, Bcl-2. The effect of lupeol on the cell viability of MCF-7 was determined by MTT and lactate dehydrogenase assays at different concentrations. The efficacy of the compound to induce cell death was analyzed using AO/EtBr staining. Phase contrast microscopic analysis provided the changes in cell morphology of the compound treated normal breast cells (MCF-10A) and MCF-7 cells. The expression of Bcl-2 and Bcl-xL proteins in the normal, cancer and lupeol treated cancer cell was analyzed by western blotting. Lupeol induced an effective change in the cell viability of MCF-7 cells with IC50 concentration as 80 μM. Induction of cell death, change in cell morphology and population of the cancer cells was observed in the lupeol treated cells, but the normal cells were not affected. The compound effectively downregulated Bcl-2 and Bcl-xL protein expressions, which directly contribute for the induction of MCF-7 cell apoptosis. Conclusion: Thus, lupeol acts as an anticancer agent against MCF-7 cells and is a potent phytodrug to be explored further for its cytotoxic mechanism.