Martine Amiot

A lymphocyte molecule implicated in lymph node homing is a member of the cartilage link protein family

Monoclonal antibodies in the Hermes family recognize a lymphocyte structure that participates in lymphocyte adhesion to endothelium and has been suggested to be the human homolog of the murine Mel-14 lymph node homing receptor. Recently, antibodies against the Hermes antigen, the polymorphic glycoprotein Pgp-1 antigen, and the broadly expressed CDw44 antigen have been shown to recognize the same structure. In this work, cDNA clones encoding the CDw44 antigen were isolated and expressed in COS cells. Two forms were identified: a lymphoid form expressed in hematopoietic cells, and an epithelial form weakly expressed in normal epithelium but highly expressed in carcinomas. The extracellular domain of CDw44 bears homology to cartilage link proteins and a related segment of proteoglycan core protein. However, comparison with the recently identified sequence of the Mel-14 antigen shows that CDw44 and Mel-14 are unrelated.

The hematopoietic and epithelial forms of CD44 are distinct polypeptides with different adhesion potentials for hyaluronate-bearing cells.

CD44 is a polymorphic integral membrane protein which recognizes hyaluronate and whose proposed roles encompass lymphocyte activation, matrix adhesion and the attachment of lymphocytes to lymph node high endothelial venules (HEVs). Immunochemical and RNA blot data have supported the existence of two forms of CD44: a hematopoietic form expressed by cells of mesodermal origin (and by some carcinoma cell lines) and an epithelial form weakly expressed by normal epithelium but highly expressed by carcinomas. This report describes the isolation of a cDNA encoding a distinct CD44 polypeptide expressed by epithelial cells. Re‐expression of each form of CD44 in a B cell line allowed cells transfected with the hematopoietic but not the epithelial form to bind to viable rat lymph node HEV cells in primary culture.

IL-6 up-regulates Mcl-1 in human myeloma cells through JAK / STAT rather than Ras / MAP kinase pathway

Mcl‐1 is an anti‐apoptotic member of the Bcl‐2 family which is tightly regulated during myeloid and B cell differentiation. We have recently reported that Mcl‐1 is expressed in human myeloma cells and that Mcl‐1 and Bcl‐xL expression are correlated. In the current study, we demonstrate that IL‐6, a survival factor for the human myeloma cell line MDN, rapidly up‐regulates Mcl‐1 whereas it has no effect on Bcl‐2 protein level. In MDN cells, IL‐6 induces both extracellular signal‐regulated protein kinase (ERK)1,2 and STAT3 activation whereas STAT1 and STAT5 activation remains undetectable. Furthermore, while investigating the IL‐6 signaling pathway leading to Mcl‐1 up‐regulation, we show that a janus kinase (JAK)‐2 inhibitor is able to inhibit both STAT3 activation and Mcl‐1 up‐regulation whereas an MAP/ERK kinase (MEK) inhibitor has no effect. In conclusion, our data suggest the involvement of the JAK / STAT pathway but not of the Ras / mitogen‐activated protein (MAP) kinase pathway in IL‐6‐induced Mcl‐1 up‐regulation.

Zoledronate Is a Potent Inhibitor of Myeloma Cell Growth and Secretion of IL-6 and MMP-1 by the Tumoral Environment

Bisphosphonates have recently been introduced in the therapeutic armamentarium for the long‐term treatment of patients with multiple myeloma (MM). These pyrophosphate analogs not only reduce the occurrence of skeletal‐related events but also provide patients with a clinical benefit and improve the survival of some of them. We investigated the effects of two bisphosphonates, pamidronate and zoledronate, on both myeloma cells and bone marrow stromal cells (BMSCs). We show here that both bisphosphonates induce both myeloma cell and BMSC apoptosis. Furthermore, at lower concentrations, they induce a significant inhibition (40% and 60%, respectively) of the constitutive production of interleukin‐6 (IL‐6) by BMSCs. We have recently shown that BMSCs produce MMP‐1, the major metalloproteinase involved in the initiation of bone resorption, production up‐regulated by IL‐1β. Here, we demonstrate that zoledronate significantly inhibits MMP‐1 production by BMSCs stimulated with IL‐1β more efficiently than pamidronate. However, zoledronate and to a lesser extent pamidronate are responsible for an up‐regulation of MMP‐2 secretion by BMSCs. MMP‐2 is involved both in bone resorption and in the metastatic process. In conclusion, the apoptosis of myeloma cells and BMSCs and the inhibition of both IL‐6 and MMP‐1 production induced by bisphosphonates, mainly zoledronate, could have antitumoral effects in patients with MM. However, the up‐regulation of MMP‐2 secretion observed in vitro suggests a putative risk of tumor cell dissemination in vivo when using these new potent bisphosphonates. This potentially deleterious effect could be abolished by combining bisphosphonates with metalloproteinase inhibitors.

Mcl-1 is overexpressed in multiple myeloma and associated with relapse and shorter survival

We and others have shown that Mcl-1 was essential for the survival of human myeloma cells in vitro. Furthermore, this antiapoptotic protein is upregulated by interleukin-6, which plays a critical role in multiple myeloma (MM). For these reasons, we have evaluated the expression of Mcl-1 in vivo in normal, reactive and malignant plasma cells (PC), that is, myeloma cells from 51 patients with MM and 21 human myeloma cell lines (HMCL) using flow cytometry. We show that Mcl-1 is overexpressed in MM in comparison with normal bone marrow PC. In total, 52% of patients with MM at diagnosis (P=0.017) and 81% at relapse (P=0.014 for comparison with diagnosis) overexpress Mcl-1. Of note, only HMCL but not reactive plasmacytoses have abnormal Mcl-1 expression, although both PC expansions share similar high proliferation rates. Of interest, Bcl-2 as opposed to Mcl-1, does not discriminate malignant from normal PC. Finally, the level of Mcl-1 expression is related to disease severity, the highest values at diagnosis being associated with the shortest event-free survival (P=0.002). In conclusion, Mcl-1, which has been shown to be essential for the survival of human myeloma cells in vitro, is overexpressed in vivo in MM in relation with relapse and shorter survival. Mcl-1 represents a potential therapeutical target in MM.

Noxa up-regulation and Mcl-1 cleavage are associated to apoptosis induction by bortezomib in multiple myeloma.

Targeting the ubiquitin-proteasome pathway has emerged as a potent anticancer strategy. Bortezomib, a specific proteasome inhibitor, has been approved for the treatment of relapsed or refractory multiple myeloma. Multiple myeloma cell survival is highly dependent on Mcl-1 antiapoptotic molecules. In a recent study, proteasome inhibitors induced Mcl-1 accumulation that slowed down their proapoptotic effects. Consequently, we investigated the role of Bcl-2 family members in bortezomib-induced apoptosis. We found that bortezomib induced apoptosis in five of seven human myeloma cell lines (HMCL). Bortezomib-induced apoptosis was associated with Mcl-1 cleavage regardless of Mcl-1L accumulation. Furthermore, RNA interference mediated Mcl-1 decrease and sensitized RPMI-8226 HMCL to bortezomib, highlighting the contribution of Mcl-1 in bortezomib-induced apoptosis. Interestingly, an important induction of Noxa was found in all sensitive HMCL both at protein and mRNA level. Concomitant to Mcl-1 cleavage and Noxa induction, we also found caspase-3, caspase-8, and caspase-9 activation. Under bortezomib treatment, Mcl-1L/Noxa complexes were highly increased, Mcl-1/Bak complexes were disrupted, and there was an accumulation of free Noxa. Finally, we observed a dissociation of Mcl-1/Bim complexes that may be due to a displacement of Bim induced by Noxa. Thus, in myeloma cells, the mechanistic basis for bortezomib sensitivity can be explained mainly by the model in which the sensitizer Noxa can displace Bim, a BH3-only activator, from Mcl-1, thus leading to Bax/Bak activation.

Mcl-1 and Bcl-xL are co-regulated by IL-6 in human myeloma cells

Multiple myeloma (MM) is a slowly proliferative malignancy in which malignant plasma cells accumulate within the bone marrow. The expression of several anti‐apoptotic proteins was evaluated by immunoblotting in human myeloma cell lines and in highly purified native myeloma cells. Expression of Bcl‐xL, Mcl‐1 and Bcl‐2 was found in most of the samples; expression of Bcl‐xL and Mcl‐1 seemed to be related on myeloma cells. In a system of apoptosis by growth factor deprivation on myeloma cells, we showed that the effect of Bcl‐2 seemed minimal whereas Mcl‐1 and Bcl‐xL were tightly regulated by interleukin (IL)‐6. These findings underline the important role of Mcl‐1 and Bcl‐xL instead of Bcl‐2 in IL‐6‐induced survival of myeloma cells.

The absence of CD56 (NCAM) on malignant plasma cells is a hallmark of plasma cell leukemia and of a special subset of multiple myeloma

In this study, we show that malignant plasma cells from patients with either primary (n = 12) or secondary (n = 15) plasma cell leukemia (PCL) do not express CD56 at all, neither in the bone marrow nor the peripheral blood in 81% of cases. On the other hand, multiple myeloma (MM) at diagnosis overexpress it in 63 of 94 (67%) cases (P = 0.0001). In three secondary PCL evaluated serially, CD56 was also lacking at diagnosis showing that CD56 is not downregulated at the end stage of the disease but rather not upregulated in this subset of patients. This last concept is strengthened by the observation that 29% of MM patients lacking CD56 or weakly expressing it at diagnosis present a detectable leukemic phase vs 11% only in CD56+ MM (P = 0.06). Forty percent of all the CD56−/weak malignant plasma cell disorders present or develop a leukemic phase vs only 15% of CD56+ cases (P < 0.008). cd56−/weak MM subset is also associated with a significantly less aggressive osteolytic potential (P = 0.012). We conclude that the lack or weak expression of CD56 is a characteristic feature of PCL but also delineates a special subset of MM at diagnosis mainly characterized by a lower osteolytic potential and a trend for malignant plasma cells to circulate in the peripheral blood more overtly.

The Bcl-2 specific BH3 mimetic ABT-199: a promising targeted therapy for t(11;14) multiple myeloma

The Bcl-2 specific BH3 mimetic ABT-199: a promising targeted therapy for t(11;14) multiple myeloma

A pivotal role for Mcl-1 in Bortezomib-induced apoptosis.

Bortezomib is a proteasome inhibitor for the treatment of relapsed/refractory multiple myeloma (MM). Mechanisms of resistance to Bortezomib are undefined. Myeloid cell leukemia-1 (Mcl-1) is an antiapoptotic protein, which protects tumor cells against spontaneous and chemotherapy-induced apoptosis. In MM, specific downregulation of Mcl-1 induces apoptosis. Here, we examined the role of Mcl-1 in Bortezomib- and doxorubicin-induced apoptosis. We demonstrate that Bortezomib, but not doxorubicin, triggers caspase-dependent generation of a 28 kDa Mcl-1-fragment, in several MM cell lines, including MM.1S cells. Conversely, transient transfection of MM.1S cells with a previously reported 28 kDa Mcl-1128–350 fragment, but not with the Mcl-11–127 fragment, induces apoptosis. Therefore, both downregulation of full-length antiapoptotic Mcl-1, as well as Bortezomib-induced generation of Mcl-1128–350 cleaved protein, contribute to MM cell apoptosis. To verify further these findings, we next compared effects triggered by Bortezomib, doxorubicin and melphalan in Mcl-1wt/wt and Mcl-1Δ/null murine embryonic fibroblasts (MEFs). Our results show that Bortezomib, but not doxorubicin or melphalan, triggers Mcl-1 cleavage in Mcl-1wt/wt, but not Mcl-1Δ/null MEFs and induces sub-G1 phase cells; caspase-3 and -9, and PARP cleavage as well as morphological signs of apoptosis. Taken together, these results support an important role of Mcl-1 and a Mcl-1 fragment in Bortezomib-induced cell death in general, and in MM in particular. To prevent relapse of MM in patients treated with Bortezomib, we therefore recommend the combination of Bortezomib with agents that induce MM cell death independent of Mcl-1.