Hee Jeong Cha

Tristetraprolin regulates expression of VEGF and tumorigenesis in human colon cancer

Tristetraprolin (TTP) is an AU‐rich element‐binding protein that regulates mRNA stability. Here, we report that TTP suppress the growth of human colon cancer cells both in vivo and in vitro by regulating of the expression of vascular endothelial growth factor (VEGF). TTP protein expression in human colonic tissues was markedly decreased in colonic adenocarcinoma compared with in normal mucosa and adenoma. VEGF expression was higher in colonic adenocarcinoma than in normal mucosa and adenoma. Specific inhibition of TTP expression by RNA‐interference increased the expression of VEGF in cultured human colon cancer cells, and TTP overexpression markedly decreased it. In addition, elevated expression of TTP decreased the expression level of luciferase linked to a 3′ terminal AU‐rich element (ARE) of VEGF mRNA. Colo320/TTP cells overexpressing TTP grew slowly in vitro and became tumors small in size when xenografted s.c into nude mice. These findings demonstrate that TTP acts as a negative regulator of VEGF gene expression in colon cancer cells, suggesting that it can be used as novel therapeutic agent to treat colon cancer.

Reactive oxygen species-dependent EndoG release mediates cisplatin-induced caspase-independent apoptosis in human head and neck squamous carcinoma cells

Cisplatin is a chemotherapeutic agent that is widely used to treat cancers such as head and neck squamous cell carcinoma (HNSCC). Previously, we have reported that cisplatin induced an early caspase‐dependent apoptosis (8 hr) in a HNSCC cell, HN4. In this study, we examined a late caspase‐independent apoptosis as well as an early caspase‐dependent apoptosis in cisplatin‐treated HN4 cells. While z‐VAD‐fmk, a pan‐caspase inhibitor, blocked the caspase activities and protected cells from the early apoptosis, it did not provide protection against delayed apoptosis occurring after extended exposure (16 hr) to cisplatin, suggesting that the delayed apoptotic response in the presence of z‐VAD‐fmk was caspase‐independent. Cisplatin treatment induced reactive oxygen species (ROS) generation, loss of the mitochondrial membrane potential (MMP) and nuclear translocation of endonuclease G (EndoG). Small interfering RNA mediated‐knockdown of EndoG significantly protected cells from the delayed apoptosis induced by cisplatin in the presence of z‐VAD‐fmk. Overexpression of Bcl‐2 in HN4 cells prevented loss of MMP, nuclear translocation of EndoG and protected cells from the delayed apoptosis induced by cisplatin in the presence of z‐VAD‐fmk. Pretreatment with N‐acetyl‐L‐cysteine (NAC), a ROS scavenger, prevented both ROS generation, loss of the MMP and nuclear translocation of EndoG. Together, our data indicate that cisplatin treatment induced ROS‐mediated loss of the MMP, and, then, the nuclear translocation of EndoG, which played a crucial role in caspase‐independent apoptosis of HN4 cells in the presence of z‐VAD‐fmk. This is the first report about the involvement of EndoG in cisplatin‐induced caspase‐independent apoptosis of cells.

Tumor suppressor p53 plays a key role in induction of both tristetraprolin and let-7 in human cancer cells

Tristetraprolin (TTP) and let-7 microRNA exhibit suppressive effects on cell growth through down-regulation of oncogenes. Both TTP and let-7 are often repressed in human cancers, thereby promoting oncogenesis by derepressing their target genes. However, the precise mechanism of this repression is unknown. We here demonstrate that p53 stimulated by the DNA-damaging agent doxorubicin (DOX) induced the expression of TTP in cancer cells. TTP in turn increased let-7 levels through down-regulation of Lin28a. Correspondingly, cancer cells with mutations or inhibition of p53 failed to induce the expression of both TTP and let-7 on treatment with DOX. Down-regulation of TTP by small interfering RNAs attenuated the inhibitory effect of DOX on let-7 expression and cell growth. Therefore, TTP provides an important link between p53 activation induced by DNA damage and let-7 biogenesis. These novel findings provide a mechanism for the widespread decrease in TTP and let-7 and chemoresistance observed in human cancers.

Tristetraprolin down-regulates IL-17 through mRNA destabilization.

An excess of interleukin 17 (IL‐17) may contribute to chronic inflammatory disorders, but mechanisms that regulate IL‐17 in immune cells are unclear. Here we report that tristetraprolin (TTP) inhibits IL‐17 production in human T cell lines. Overexpression of TTP decreased the expression of IL‐17. Conversely, TTP inhibition by siRNA increased IL‐17 production. IL‐17 mRNA contains eight AREs within its 3′UTR. TTP bound directly to the IL‐17 mRNA 3′UTR at a location between the fourth and seventh AREs and enhanced decay of IL‐17 transcripts. These results suggest that TTP could control IL‐17‐mediated inflammation.

Ectopic over-expression of tristetraprolin in human cancer cells promotes biogenesis of let-7 by down-regulation of Lin28

Tristetraprolin (TTP) is a AU-rich element (ARE) binding protein and exhibits suppressive effects on cell growth through down-regulation of ARE-containing oncogenes. The let-7 microRNA has emerged as a significant factor in tumor suppression. Both TTP and let-7 are often repressed in human cancers, thereby promoting oncogenesis by derepressing their target genes. In this work, an unexpected link between TTP and let-7 has been found in human cancer cells. TTP promotes an increase in expression of mature let-7, which leads to the inhibition of let-7 target gene CDC34 expression and suppresses cell growth. This event is associated with TTP-mediated inhibition of Lin28, which has emerged as a negative modulator of let-7. Lin28 mRNA contains ARE within its 3′-UTR and TTP enhances the decay of Lin28 mRNA through binding to its 3′-UTR. This suggests that the TTP-mediated down-regulation of Lin28 plays a key role in let-7 miRNA biogenesis in cancer cells.

Subcutaneous panniculitis-like T-cell lymphoma: US and CT findings in three patients

Subcutaneous panniculitis-like T-cell lymphoma (SPTCL) is a rare disorder. We examined two females and one male with multiple soft-tissue masses in the abdominal wall. One of these three patients also had soft-tissue masses in the right thigh and right buttock. The histologic diagnosis was revealed as SPTCL in all three cases. The ultrasound (US) findings in two of these cases were diffuse, ill-defined hyperechoic areas with a linear vascular signal. The findings of the abdominal and pelvic computed tomography (CT) scanning with contrast enhancement were multiple enhancing nodules with an infiltrative pattern of peripheral subcutaneous fat layer in all three cases. We report US and CT findings of SPTCL in these three patients.

Cutaneous Polyarteritis Nodosa Presented with Digital Gangrene: A Case Report

Cutaneous polyarteritis nodosa (CPAN) is an uncommon form of vasculitis involving small and medium sized arteries of unknown etiology. The disease can be differentiated from polyarteritis nodosa by its limitation to the skin and lack of progression to visceral involvement. The characteristic manifestations are subcutaneous nodule, livedo reticularis, and ulceration, mostly localized on the lower extremity. Arthralgia, myalgia, peripheral neuropathy, and constitutional symptoms such as fever and malaise may also be present. We describe a 34-yr-old woman presented with severe ischemic change of the fingertip and subcutaneous nodules without systemic manifestations as an unusual initial manifestation of CPAN. Therapy with corticosteroid and alprostadil induce a moderate improvement of skin lesions. However, necrosis of the finger got worse and the finger was amputated.

Follicular Dendritic Cell Sarcoma: A Case Report and Review of the Literature

Follicular dendritic cells (FDC) are non-lymphoid, non-phagocytic accessory cells of the immune system and these cells are essential for antigen presentation and regulation of the reactions in germinal centers. Follicular dendritic cell sarcoma (FDCS) is a rare neoplasm that shows a low-to-intermediate malignant potential. The most commonly involved sites are the lymph nodes, but FDCS may also occur at a variety of extranodal sites, including the oral cavity, tonsils, gastrointestinal tract and liver. We describe here a 79-year-old woman who had FDCS with extensive lymph node involvement, dry cough, and an itching sensation. The patient improved after systemic chemotherapy.

Tristetraprolin down-regulates IL-23 expression in colon cancer cells

Interleukin 23 (IL-23) is an inflammatory cytokine that plays an important role in tumor promotion. Expression of IL-23 is increased in cancer cells and correlates with tumor progression. However, the mechanisms regulating IL-23 expression in cancer cells are still unclear. Here we report that tristetraprolin (TTP), an AU-rich element (ARE)-binding protein, inhibits IL-23 production in CT26 mouse colon cancer cells. Overexpression of TTP decreased the stability of IL-23 mRNA and the expression level of IL-23 in CT26 cells. Conversely, inhibition of TTP by siRNA increased IL-23 production. TTP destabilized a luciferase mRNA reporter containing the IL-23 mRNA 3’UTR, which contains five AREs. Analyses of deletion and point mutants of the IL-23 mRNA 3’UTR demonstrated that the ARE cluster between the third and fifth AREs was responsible for TTP-mediated destabilization of IL-23 mRNA. A RNA electrophoretic mobility shift assay confirmed that TTP binds to this ARE cluster. Taken together, these results demonstrate that TTP acts as a negative regulator of IL-23 gene expression in mouse colon cancer cells and suggest its potential application as a novel therapeutic target to control IL-23-mediated tumor promotion.

A Case of Atypical Skull Base Osteomyelitis with Septic Pulmonary Embolism

Skull base osteomyelitis (SBO) is difficult to diagnose when a patient presents with multiple cranial nerve palsies but no obvious infectious focus. There is no report about SBO with septic pulmonary embolism. A 51-yr-old man presented to our hospital with headache, hoarseness, dysphagia, frequent choking, fever, cough, and sputum production. He was diagnosed of having masked mastoiditis complicated by SBO with multiple cranial nerve palsies, sigmoid sinus thrombosis, and septic pulmonary embolism. We successfully treated him with antibiotics and anticoagulants alone, with no surgical intervention. His neurologic deficits were completely recovered. Decrease of pulmonary nodules and thrombus in the sinus was evident on the follow-up imaging one month later. In selected cases of intracranial complications of SBO and septic pulmonary embolism, secondary to mastoiditis with early response to antibiotic therapy, conservative treatment may be considered and surgical intervention may be withheld.