Characterization Of SERCA2b As The Target Protein Of Curcumin And Its Role In Human Liposarcoma

In Chapter One, we discovered that curcumin could selectively inhibit the survival rate of human liposarcoma cells but not normal adipose derived cells, which was quite different from the classical chemotherapeutic drugs used in clinical treatment. Curcumin induced Capsase8/3 dependent apoptosis in human liposarcoma SW872 cells but not Caspase9. Curcumin binds directly with and inhibits the activity of sarcoplasmic/endoplasmic reticulum Ca2+-ATPase2(SERCA2), which is highly expressed in human liposarcoma. The disfunction of SERCA2b made by curcumin disrupted the balance of Ca2+, leading to ER stress in liposarcoma cells. CHOP as a transcription factor of TRAIL-R2(DR5) increases during cells undergo ER stress, the enrichment of DR5 on the surface of cells will induce Caspase 8 dependent apoptosis. Different SERCA family members expression in different tissues, in our studies, we discovered for the first time that 66.7% of 24 human liposarcoma samples expression high level of SERCA2, which is also correlative with the malignant degree of these samples. For liposarcoma roots in transformed normal stromal tissue, and the malignant degree of liposarcoma has close relationship with its differentiation degree, In Chapter Two, we tried to identify the possible function of SERC2b In the differentiation of liposarcoma cells. As we know, liposarcoma cell line could also differentiate in vivo as normal adipose cells. Although it is hard to induce liposarcoma cells to differentiate into mature adipose cells, some differentiation makers will also enhance during differentiation as normal adipose cells. Stably transfected SERCA2b could induce the accumulation of ROS in SW872 cells, activating MEK/ERK pathway. Activated ERK then phosphorylated PPAR-y, which prevented PPAR-y entering into nulei to transcript downstream genes, leading to the resistance of liposarcoma cells differentiation. Interestingly, we found that SERCA2b induced ERK phosphorylation in a kinase activity independent way. Consistent with previous studies, the inhibitor of SERCA2b could also induce ERK phosphorylation. All these results indicated that SERCA2b induced ROS dependent activation of ERK in a Ca2+ pump independent way. For the low metastasis ability of liposarcoma, the main clinical therapy for curing liposarcoma is surgery. However, since liposarcoma has a very high relapse rate, continual surgery will bring great pain to patients. Moreover, liposarcoma is non-sensitive to chemotherapeutic drugs treatment or radiotherapy. All these results indicated the possibility of the existence of a small group of stem cell-like cells in human liposarcoma, which be the initiator of relapse. In Chapter Three, we firstly established a high malignant sub cell line (SW872-S) from human liposarcoma cell line SW872 by re-transplantation in nude mice. We identified that integrin α6 was high expressed in SW872-S cells. Integrin a6high population of cells revealed extremely high growth ability in vitro and in vivo, as well as the ability of colony formation and self-renew. We could also find integrin a6 positive cells in liposarcoma samples from patients with relapse, but not in well-differentiated liposarcoma samples or normal adipose tissues. Our result indicated that integrin a6 could be used as important marker for identifying stem cell-like cells in human liposarcoma. For liposarcoma developed from adipose tissue, we then examined the reported stem cell markers expressing on the surface of adipose stem cells. We detected that CD 13 co-overexpression with integrin cc6, the double positive cell group exhibited highest level of BCL2, which might mediate the anti-apoptosis ability of integrin a6high cells. Consistently, CD 13 siRNA as well as its specific inhibitor selectively inhibited the survival rate of integrin α6high cells, which may contribute the therapeutic therapy targeting integrin α6high sub-population cells.It is the first time to discover the effect of curcumin on treating human liposarcoma, as well as SERCA2b, the direct interatction protein of curcumin in human liposarcoma cells. Further study proved the role played by SERCA2b in the dedifferentiation effect of liposarcoma cells. Moreover, we identified and characterized a small population of stem cell-like cells in human liposarcoma. These findings illustrate the mechanism of recurrence and dedifferentiation of human liposarcoma, and also guide significance for development of anti-liposarcoma drugs.