Oculocutaneous albinism types 1 and 3 are ER retention diseases: mutation of tyrosinase or Tyrp1 can affect the processing of both mutant and wild-type proteins.

Various types of oculocutaneous albinism (OCA) are associated with reduced pigmentation in the skin, hair, and eyes that results from mutations in genes involved in melanin synthesis. Immortal mouse melanocyte lines (melan-a, melan-b, and melan-c) provide opportune models with which to investigate the etiology of two different types of OCA (types I and III), which arise from mutations in Tyr and Tyrp1, respectively. We compared intracellular processing, sorting, and degradation of tyrosinase and Tyrp1, and the effects on their catalytic function and melanin synthesis, in these wild-type and mutant melanocytes. A mutation in either Tyr or Tyrp1 increased the time of association of tyrosinase and Tyrp1 with calnexin and Bip, which in turn resulted in the retention of these mutant products in the ER. A mutation in either gene selectively enhanced the duration and efficiency of chaperone interactions (even with the wild-type protein in the mutant melanocytes) and markedly slowed their transport to melanosomes. These results show that OCA1 and OCA3 are (in some cases, at least) ER retention diseases wherein a mutation in one melanogenic protein affects the maturation and stability of the other in the melanogenic pathway.

A model for melanosome biogenesis based on the purification and analysis of early melanosomes.

Melanosome biogenesis and function were studied after purification of early stage melanosomes and characterization of specific proteins sorted to that organelle. Melanosomes were isolated from highly pigmented human MNT1 melanoma cells after disruption and initial separation by sucrose density gradient centrifugation. Low-density sucrose fractions were found by electron microscopy to be enriched in stage I and stage II melanosomes, and these fractions were further separated and purified by free flow electrophoresis. Tyrosinase and dopachrome tautomerase (DCT) activities were found exclusively in stage II melanosomes, even though DCT (and to some extent tyrosinase) proteins were sorted to stage I melanosomes. Western immunoblotting revealed that these catalytic proteins, as well as TYRP1, MART1, and GP100, were cleaved and inactivated in stage I melanosomes. Proteolytic cleavage was critical for the refolding of GP100 within the melanosomal milieu, and subsequent reorganization of amorphous stage I melanosomes into fibrillar, ovoid, and highly organized stage II melanosomes appears to stabilize the catalytic functions of melanosomal enzymes and allows melanin biosynthesis to begin. These results provide a better understanding of the structural features seen during melanosome biogenesis, and they yield further clues as to the physiological regulation of pigmentation.

[A biological and morphological study of ovoid and spindle cells in malignant fibrous histiocytomas].

To clarify the histogenesis of malignant fibrous histiocytoma (MFH), ovoid and spindle cells, the major components of this tumor, were biologically and morphologically studied using the following methods: (1) flow cytometric nuclear DNA analysis, (2) argyrophil staining for nucleolar organizer regions (Ag-NORs), (3) separation of MFH cells into the two types described above using a flow cytometric cell sorting system, (4) electron microscopic morphological observation, and (5) immunohistochemical examination. Specimens were obtained from 24 cases of soft-tissue MFH and 7 cases of MFH in the bone, which were treated in our institute. In ovoid cells, aneuploid pattern was shown by nuclear DNA analysis and high proliferation activity was found on Ag-NORs staining. Ultrastructural analysis showed that the ovoid cells had malignant characteristics and were presumedly histiocytic in origin. Immunohistochemical examination also, supported histiocytic origin. However, spindle cells were not identified as malignant tumor cells by the various methods described above. Although the histogenesis of MFH remains to be elucidated, these findings provide interesting information.

[The progression of renal damage in reflux nephropathy--clinical analysis of proteinuria in children with vesicoureteral reflux].

To clarify the mechanism for reflux nephropathy to progress to irreversible or marginal renal damages, this study was conducted. We studied 57 cases of VUR in children followed-up more than 3 years after anti-reflux operation and investigated the correlation between changes of urinary protein excretion and clinical data. In general, proteinuria is the most important feature heralding a poor outcome in patients with reflux nephropathy. 9 cases (15.8%) in our series were positive of proteinuria postoperatively. In this positive group, scarring grade had been higher and renal size had been smaller significantly before operation than in other group. From these facts, it would appear that prognosis of refluxing kidney was determined by volume of remnant kidney, and glomerular hyperfiltration of remnant nephron would affect the progression of reflux nephropathy. According to the relationship between changes of urinary protein excretion and scarring grade or renal size, poor prognosis (proteinuria will worsen) would be more than 5 of scarring grade score (cumulation of bilateral scarring grades, Smellie's a = 1, b = 2, c = 3, d = 4) and less than -4S.D. in cumulative renal ratio preoperatively. Then border to progression in reflux nephropathy was between 2 and 4 of scarring grade score, and between -2S.D, and -4S.D. in cumulative renal ratio. In this marginal progression urinary protein excretion and GFR were found to be 100-300 mg/day and 60-75 ml/min, respectively.