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A second class II AP endonuclease, APEX2, possesses strong 3′–5′ exonuclease and 3′-phosphodiesterase activities but only very weak AP-endonuclease activity. APEX2 associates with proliferating cell nuclear antigen (PCNA), and the progression of S phase of the cell cycle is accompanied by its expression. APEX2-null mice exhibit severe dyslymphopoiesis in thymus as well as moderate dyshematopoiesis and growth retardation. Comparative gene expression profiling of wild-type and APEX2-null mice using an oligonucleotide microarray revealed that APEX2-null thymus has significantly altered gene expression profiles, reflecting its altered populations of thymocytes. Beyond these altered populations, APEX2-null thymus exhibits significant alterations in expression of genes involved in DNA replication, recombination and repair, including Apex1, Exo1 and Fen1 as well as master genes for the DNA damage response, such as E2f1, Chek1, and proapoptotic genes. We therefore examined the extent of DNA strand breakage, and found that both of single-strand breaks detected as comets and double-strand breaks detected as γH2AX foci were significantly higher in frequency in most APEX2-null thymocytes compared to wild-type thymocytes. This higher frequency of DNA breaks was accompanied by increased expression of PCNA and increased phosphorylation of p53 at Ser23 and to a lesser extent, at Ser18. The present study clearly demonstrates that APEX2-null lymphocytes have a higher frequency of DNA breaks, indicating that APEX2 may play an important role(s) during their generation and/or repair.

APEX2/APE2 is a secondary mammalian apurinic/apyrimidinic endonuclease that associates with proliferating cell nuclear antigen (PCNA), and the progression of S phase of the cell cycle is accompanied by its expression. To determine the biologic significance of APEX2, we established APEX2-null mice. These mice were about 80% the size of their wild-type littermates and exhibited a moderate dyshematopoiesis and a relatively severe defect in lymphopoiesis. A significant accumulation of both thymocytes and mitogen-stimulated splenocytes in G2/M phase was seen in APEX2-null mice compared with the wild type, indicating that APEX2 is required for proper cell cycle progression of proliferating lymphocytes. Although APEX2-null mice exhibited an attenuated immune response against ovalbumin in comparison with wild-type mice, they produced both antiovalbumin immunoglobulin M (IgM) and IgG, indicating that class switch recombination can occur even in the absence of APEX2. (Blood. 2004;104: 4097-4103)

In mammalian cells, more than one genome in a single cell has to be maintained throughout the entire life of the cell, namely, one in the nucleus and the other in the mitochondria. The genomes and their precursor nucleotides are highly exposed to reactive oxygen species, which are inevitably generated as a result of the respiratory function in mitochondria. To counteract such oxidative damage in nucleic acids, cells are equipped with several defense mechanisms. Modified nucleotides in the nucleotide pools are hydrolyzed, thus avoiding their incorporation into DNA or RNA. Damaged bases in DNA with relatively small chemical alterations are mainly repaired by the base excision repair (BER) system, which is initiated by the excision of damaged bases by specific DNA glycosylases. MTH1 protein hydrolyzes oxidized purine nucleoside triphosphates, such as 8-oxo-dGTP, 8-oxo-dATP, and 2-hydroxy (OH)-dATP to the monophosphates, and MTH1 are located in the cytoplasm, mitochondria, and nucleus. We observed an increased susceptibility to spontaneous carcinogenesis in Mth1-deficient mice and an alteration of MTH1 expression along with the accumulation of 8-oxo-dG in patients with various neurodegenerative diseases. Enzymes for the BER pathway, namely, 8-oxoG DNA glycosylase (OGG1), 2-OH-A/adenine DNA glycosylase (MUTYH), and AP endonuclease (APEX2) are also located both in the mitochondria and in the nuclei, and the expression of mitochondrial OGG1 is altered in patients with various neurodegenerative diseases. We also observed increased susceptibilities to spontaneous carcinogenesis in OGG1 and MUTYH-deficient mice. The increased occurrence of lung tumor in OGG1-deficient mice was completely abolished by the concomitant disruption of the Mth1 gene.

As previously reported, MRI is found to be useful in the evaluation of meniscal and cruciate ligament injuries. But at our institute, however, due to frequent in consistencies between MRI and arthroscopic findings, we investigated problem knees by MRI and compared the findings with those using arthroscopy subsequently performed. 28 cases with medial and lateral meniscus, and 31 cases with anterior and posterior crucial ligament were examined. The field strength of MRI was 1.0 Tesla, and images were meared by the T2 weighted gradient echo method. Sensitivity for medial meniscus, lateral meniscus, anterior cruciate ligament, and posterior cruciate ligament was 60, 38, 33, and 20 percent respectively, specificity was 78, 90, 91, and 89 percent respectively, and accuracy was 75, 75, 74, and 77 percent respectively. These values are lower compared with other reports. Diagnoses of meniscal and cruciate ligament injuries from magnetic resonance imaging of the knee at our institute are not confidential. For improvement, the scanning and imaging methods, must be changed and a new sophisticated MRI scanner is desirable.

There are only a few reports following the osteomyelitis using MRI. We experienced a case of bacterial osteomyelitis of the femur which formed a broad subperiosteal abscess.We used MRI for the diagnosis and follow up and found it to be useful.The case was a 12 year old male, who presented with a 40°C fever and swelling and local heat of his right thigh were observed. On blood examination, WBC number was decreased, with a shift to the left, and CRP was strongly positive. MRI T2WI showed a broad high intensity area in the subperiosteal space. Puncture showed bloody abscess and the patient was hospitalized for examination and treatment. Bacterial culture of the abscess and blood were performed and both of which were positive for Staphylocossus aureus.We performed an irrigatim of the abcsess fenestration of the bone, and continuos intramedullary drip infusion of antibiotics. MRI was also useful for observation of the recovery stage.

Lesions of the rheumatoid cervical spine are mainly observed in the upper cervical spine. We experienced a case of rheumatoid cervical spondylosis assumed to be traceable to Luschka's joint of the lower cervical spine. The case was a 50 years-old female who had suffered from rheumatoid arthritis for 18 years. On 25th May, 1993, she developed numbness of her left hand. On 29th July, 1993, muscle weakness of her left lower extremity and urinary retention appeared. On admission, manual muscle testing revealed the bilateral upper extremities to be 0 to 1, right lower extremity 1 to 3, left lower extremity 5. Sensory disturbance was observed on bilateral upper extremities and left foot. Hyperreflexia of the deep tendon reflexes of the upper and lower extremities were observed. X-ray films showed narrowing of C4/5 disc space and anterior subluxation of C4. Myelography showed compression from the anterior and left side at C4/5. CT-myelography showed destructive change of bone and compression from antero-left side at C4/5. Postero-lateral fusion and anterior decompressive fusion were performed. During Surgery, bone destruction assumed to be traceable to rheumatoid granulation and posterior prominence of granulation tissue were observed. Post surgery, neurological symptoms remarkably improved.

In mammalian cells, more than one genome in a single cell has to be maintained throughout the entire life of the cell, namely, one in the nucleus and the other in the mitochondria. The genomes and their precursor nucleotides are highly exposed to reactive oxygen species, which are inevitably generated as a result of the respiratory function in mitochondria. To counteract such oxidative damage in nucleic acids, cells are equipped with several defense mechanisms. Modified nucleotides in the nucleotide pools are hydrolyzed, thus avoiding their incorporation into DNA or RNA. Damaged bases in DNA with relatively small chemical alterations are mainly repaired by the base excision repair (BER) system, which is initiated by the excision of damaged bases by specific DNA glycosylases. MTH1 protein hydrolyzes oxidized purine nucleoside triphosphates, such as 8-oxo-dGTP, 8-oxo-dATP, and 2-hydroxy (OH)-dATP to the monophosphates, and MTH1 are located in the cytoplasm, mitochondria, and nucleus. We observed an increased susceptibility to spontaneous carcinogenesis in Mth1-deficient mice and an alteration of MTH1 expression along with the accumulation of 8-oxo-dG in patients with various neurodegenerative diseases. Enzymes for the BER pathway, namely, 8-oxoG DNA glycosylase (OGG1), 2-OH-A/adenine DNA glycosylase (MUTYH), and AP endonuclease (APEX2) are also located both in the mitochondria and in the nuclei, and the expression of mitochondrial OGG1 is altered in patients with various neurodegenerative diseases. We also observed increased susceptibilities to spontaneous carcinogenesis in OGG1 and MUTYH-deficient mice. The increased occurrence of lung tumor in OGG1-deficient mice was completely abolished by the concomitant disruption of the Mth1 gene.

We isolated a mouse cDNA encoding APEX2 protein and demonstrated that APEX2 binds to PCNA. The level of Apex2 mRNA was high in the thymus, bone marrow, spleen, and kidney in adult mice. Apex2 consists of six exons and is flanked on the 3' end by Alas2 on X chromosome 63.0. Furthermore, Apex2 is flanked on the 5' end by a novel gene with a 106-bp intergenic sequence. We disrupted Apex2 in embryonic stem cells derived from a male mouse, and a 55-kDa APEX2 protein was detected in the nuclei of Apex2(+) but not Apex2-disrupted cells. Immunoelectron microscopy revealed that APEX2 is also localized in the mitochondria of Apex2(+) cells. In serum-stimulated BALB/c 3T3 cells, the level of Apex2 mRNA was transiently increased and the level of APEX2 reached a maximum in the late S phase, thus indicating that APEX2 may participate in postreplicative base excision repair.