Mutant fibrinogen cleared from the endoplasmic reticulum via endoplasmic reticulum-associated protein degradation and autophagy: an explanation for liver disease

The endoplasmic reticulum (ER) quality control processes recognize and remove aberrant proteins from the secretory pathway. Several variants of the plasma protein fibrinogen are recognized as aberrant and degraded by ER-associated protein degradation (ERAD), thus leading to hypofibrinogenemia. A subset of patients with hypofibrinogenemia exhibit hepatic ER accumulation of the variant fibrinogens and develop liver cirrhosis. One such variant named Aguadilla has a substitution of Arg375 to Trp in the gamma-chain. To understand the cellular mechanisms behind clearance of the aberrant Aguadilla gamma-chain, we expressed the mutant gammaD domain in yeast and found that it was cleared from the ER via ERAD. In addition, we discovered that when ERAD was saturated, aggregated Aguadilla gammaD accumulated within the ER while a soluble form of the polypeptide transited the secretory pathway to the trans-Golgi network where it was targeted to the vacuole for degradation. Examination of Aguadilla gammaD in an autophagy-deficient yeast strain showed stabilization of the aggregated ER form, indicating that these aggregates are normally cleared from the ER via the autophagic pathway. These findings have clinical relevance in the understanding of and treatment for ER storage diseases.

Spinal manifestations of vertebral artery dissection

Among 111 patients with vertebral artery dissection (VAD), two presented with spinal manifestations: one with a C5-C6 radiculopathy and the other with a cervical myelopathy. Of 13 previously reported cases of spinal manifestations of VAD (mean age 37 years), ischemic cervical myelopathy was noted in seven; cervical radiculopathy, often at C5-C6 and primarily motor, in five; and hemorrhagic complications in one, with chest pain being part of the presentation.

Temperature and manganese as determining factors in the presence of diatom or blue-green algal floras in streams

Diatoms are usually the major component of the algal flora in many streams, although green and blue-green algae may be present. These experiments were designed to determine if high temperature or a shift in the chemical composition of the water might bring about a dominance of blue-green algae and/or green algae rather than a dominance of diatoms in the algal flora.The results of these experiments indicate that an average temperature of 34 degrees to 38 degrees C results in a shift of dominance in the algal flora from diatoms to blue-green algae. Furthermore, a blue-green and green algal flora of species typically found in organically polluted water in favored if the manganese content is a few parts per billion. If the manganese content averaged 0.02-0.043 mg/liter in the natural stream to 0.04-0.28 mg/liter in the recycled water experiment, a diatom flora remained dominant.

The myeloid zinc finger gene (MZF-1) delays retinoic acid-induced apoptosis and differentiation in myeloid leukemia cells

The myeloid zinc finger gene, MZF-1, is a hematopoietic transcription factor expressed in developing myeloid cells. To characterize further the role of MZF-1 in myelopoiesis, we used retroviral gene transduction to overexpress MZF-1 in HL-60 cells to produce HL-60-MZF-1 cells. HL-60 cells respond to retinoic acid (RA) with growth inhibition, granulocytic differentiation and apoptosis. However, HL-60-MZF-1 cells exposed to RA continue to proliferate in response to RA as evidenced by a higher percentage of cells in S phase, higher peak cell counts, and later peak cell counts. Morphologic differentiation of the RA-induced HL-60-MZF-1 cells is delayed with half as many of the HL-60-MZF-1 cells compared to the wild-type HL-60 cells that are differentiated after 3 days of RA, although both cells types responded with 80-95% mature granulocytes after 6 days of RA. Apoptosis was delayed in the MZF-1 transduced cells as measured by internucleosomal DNA fragmentation patterns, the terminal transferase end labeling reaction (TUNEL), and quantitation of fragmented DNA by the diphenylamine reaction. Several markers of differentiation were identical in both HL-60 and HL-60-MZF-1 cells including CD11b, CD33, CD34, CD13, CD16 and CD14. However, following 6 days of RA, only half as many HL-60-MZF-1 cells expressed CD18 compared to the wild-type HL-60 cells. Expression of the bcl-2 proto-oncogene transcript and protein was higher in the HL-60-MZF-1 cells compared to wild-type HL-60s and expression persisted for 5 days following RA in the HL-60-MZF-1 cells compared to only 3 days in the parental HL-60 cells suggesting that bcl-2 may contribute to the inhibition of apoptosis. Overexpression of MZF-1 had no effect on PMA-induced monocyte/macrophage differentiation of HL-60 cells. Together these findings indicate that MZF-1 can stimulate cell proliferation and delay RA-induced differentiation and apoptosis in HL-60 cells. MZF-1 may function in a similar role in myelopoiesis allowing myeloid precursors to expand their numbers before going on to terminally differentiate.

Yolk protein endocytosis by oocytes in Drosophila melanogaster: immunofluorescent localization of clathrin, adaptin and the yolk protein receptor

The process of yolk protein (YP) uptake by developing oocytes in Drosophila melanogaster has been investigated by immunofluorescent localization of the endocytosis proteins, clathrin, alpha-adaptin and the putative yolk protein receptor (YP receptor). Data suggests that YPs from the follicle cells are trafficked into the oocyte during early stages of vitellogenesis, and that hemolymph YPs are sequestered by nurse cells adjacent to the developing oocyte during late stages of vitellogenesis. Yolk proteins were immunolocalized to both follicle cells and nurse cells during these processes. Diapausing female Drosophila melanogaster undergo a pre-vitellogenic arrest of ovarian development associated with the absence of ovarian alpha-adaptin, clathrin and putative YP receptor. Diapause termination by transfer of whole animals from 11 degrees C to 25 degrees C, or by 20-hydroxyecdysone injection, results in the appearance of immunopositive material in the nurse cells for all three proteins between 12 h and 16 h post upshift and within four days of injection. Immunopositive material was not noted in the follicle cells during diapause termination. In vitro warming of diapausing ovaries, or incubation in the presence of 1 &mgr;M 20-hydroxyecdysone failed to initiate early vitellogenic development suggesting that diapause termination requires factor(s) external to the ovary. Western blotting analysis of extracts of 24 h post-eclosion wild type and ap(56f) females identified putative yolk protein receptor with a molecular weight of 208 kDa and clathrin with a molecular weight of 178 kDa.

An unusual complication of nasolacrimal duct probing

A 4-mm segment of the tip of a 0000 probe broke off inside the nasolacrimal duct of an 11-month-old girl during probing for congenital nasolacrimal duct obstruction. Despite numerous attempts, the tip could not be extracted. Examination of the 000 end of the double-ended probe showed a narrow neck approximately 4 mm from the bulbous tip. Choosing an appropriate probe design, inspecting the probe before use, and selecting the appropriate probe size will help prevent this unusual complication.