Two functionally different domains of rabphilin-3A, Rab3A p25/smg p25A-binding and phospholipid- and Ca(2+)-binding domains

Rabphilin-3A is a putative target molecule for rab3A p25/smg p25A, which is a member of a ras p21-related small GTP-binding protein and implicated in neurotransmitter release from the synapse. Rabphilin-3A has two copies of an internal repeat that are homologous to the C2 domains of protein kinase C, synaptotagmin, and phospholipase A2, which are known to bind to phospholipid in a Ca(2+)-dependent manner. In the current study, we have investigated the functional domains or rabphilin-3A by use of three recombinant proteins as follows: full rabphilin-3A (1-704 amino acids), an N-terminal fragment (1-280 amino acids), and a C-terminal fragment containing the C2 domains (281-704 amino acids). Both rabphilin-3A and the C-terminal fragment bound to phospholipid in the presence of Ca2+, but the N-terminal fragment did not bind to phospholipid. 45Ca2+ bound to rabphilin-3A and the C-terminal fragment only in the presence of phospholipid but did not bind to the N-terminal fragment. The GTP gamma S-bound form of rab3A p25 bound to both rabphilin-3A and the N-terminal fragment but did not bind to the C-terminal fragment. These results indicate that rabphilin-3A has at least two functionally different domains, the N-terminal rab3A p25-binding and C-terminal phospholipid- and Ca(2+)-binding domains.

Acute promyelocytic leukemia with t(15;17) abnormality after chemotherapy containing etoposide for Langerhans cell histiocytosis

BACKGROUND

Epipodophyllotoxins, etoposide and teniposide, have been shown to be implicated in the development, of acute myelogenous leukemia in patients treated for solid tumors or acute lymphoblastic leukemia. Etoposide has been shown to be an effective agent against Langerhans cell histiocytosis (LCH) and has gained wider use recently for first-line and salvage chemotherapy in cases of systemic LCH.

METHODS

The authors report two patients with secondary acute promyelocytic leukemia (APL) with a t(15;17) abnormality after chemotherapy that included etoposide for the treatment of LCH.

RESULTS

Patient 1, a 6-year-old girl, had APL develop 11 months after cessation of therapy that included vinblastine, prednisolone, and etoposide (9600 mg/m2 in total dose) for LCH. Patient 2, a 3-year-old girl, had APL develop 9 months after cessation of therapy that included vincristine, methotrexate, prednisolone, cyclophosphamide (10,800 mg/m2), and etoposide (4800 mg/m2) for LCH.

CONCLUSIONS

The authors have experience with four patients treated with etoposide for LCH and suggest that there is a predisposition to secondary APL with t(15;17) for patients with LCH treated with etoposide. The authors warn against the imprudent use of etoposide as a first-line therapy for LCH.

New E2A/PBX1 fusion transcript in a patient with t(1;19)(q23;p13) acute lymphoblastic leukemia

About 25% of the children with pre-B cell acute lymphoblastic leukemia (ALL) have a chromosomal translocation of t(1;19)(q23;p13). This translocation juxtaposes the E2A gene on chromosome 19 to the PBX1 gene on chromosome 1, leading to production of a fusion transcript. The fusion sites of the E2A and PBX1 coding sequence have been identical among all cases of t(1;19) ALL studied so far. Here we described a new fusion site of the E2A and PBX1 genes, which was detected in the leukemic blasts of a child with t(1;19) pre-B ALL using the reverse transcriptase polymerase chain reaction and direct sequencing. The fusion site was located just upstream of the DNA binding domain of the E2A gene, and was close to a homeodomain of the PBX1 gene.

[Detection of minimal residual disease using reverse transcriptase polymerase chain reaction technique]

Polymerase chain reaction (PCR) is a highly sensitive technique to detect minimal residual disease (MRD) of hematological malignancy by amplifying tumor specific nucleotide sequences. When breakpoint is located over large lesions of genomic DNA, like t(9;22) leukemia, PCR amplifying cDNA of chimeric mRNA, called reverse transcriptase PCR (RT-PCR), can be utilized. We applied this method for the detection of MRD in patients with t(1; 19) acute lymphoblastic leukemia. RT-PCR detection of MRD in patients with leukemia might be useful for estimating of the depth of remission, for disclosing preclinical relapse, and for evaluating the efficacy of in vitro purging in autologous bone marrow transplantation.

[T4 carcinoma of the oral cavity responsive to bilateral 5-FU intra-arterial infusion and simultaneous irradiation]

5-FU intra-arterial infusion and simultaneous irradiation can cure head and neck cancer without leaving any functional disturbance. Catheters were inserted into the bilateral superficial temporal arteries in a case of T4 carcinoma of the oral cavity, and this treatment was performed. The patient was a 54-year-old male with squamous cell carcinoma involving the right tonsil, right and left sides of the soft palate, the uvula, right gingiva, right lingual margin, and right buccal mucous membrane. The right soft palate was partially defective. The total dose of intra-arterial 5-FU was 4,000 mg on the right side and 2,600 mg on the left side, and the total dose of irradiation was 40 Gy. After this treatment, residual cancer was found on the right margin of the uvula only. Due to the defect in the soft palate, the effect of intra-arterial infusion was considered to be insufficient for this region, and it was excised together with the surrounding tissue. Rhinolalia aperta remains, but there is no dysphagia, and the course has been good with no evidence of recurrence so far. When it is found that a catheter cannot be readily inserted, it can usually be inserted properly by using a guide wire. For fixing the catheter, a satisfactory result is obtained by cutting the protruding end to 15-20 cm, attaching a connector, and suturing it to the skin of the temporal region.