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Expression of the genes encoding the beta/A4 amyloid protein precursor (APP) and microtubule-associated protein tau was studied in an embryonal carcinoma cell line (P19) that differentiates in vitro into cholinergic neurons after treatment with retinoic acid. Expression of APP increased 34- (mRNA) and 50-fold (protein) during neuronal differentiation; APP-695 accounted for most of this increase. These remarkable increases in APP expression coincided with a proliferation of neuronal processes and with an increase in content of tau mRNA. Moreover, subsequent decreases in the levels of APP and tau mRNA coincided with the onset of the degeneration of the neuronal processes. Immunocytochemical staining suggested that greater than 85% of the P19-derived neurons are cholinergic and that APP is present in the neuronal processes and cell bodies. These results suggest that APP may play an important role in construction of neuronal networks and neuronal differentiation and also indicate that this embryonal carcinoma cell line provides an ideal model system to investigate biological functions of APP and the roles of APP and tau protein in development of Alzheimer's disease in cholinergic neurons.

Proteoglycans (PGs) incorporated into cell layer and secreted into media were characterized during retinoic acid-induced neuronal differentiation of cultured P19 murine embryonal carcinoma cells. Heparan sulfate significantly increased (P < 0.01) in cell layer following neuronal differentiation of P19 cells by 3.9-fold. CL-4B gel chromatography revealed the major PGs present in cell layer of stem cells eluted as a broad peak with a Kav = 0.65, and was susceptible to chondroitin ABC lyase. The chondroitin ABC lyase resistant material eluted as a broad peak between Kav = 0.40 and Kav = 0.60, and was only partially digested with heparitinase/heparinase (with resistant material eluting at Kav = 0.70). Therefore, the cell layer of stem cells contained primarily chondroitin sulfate/dermatan sulfate (CS/DS) PGs, with lesser amounts of heparan sulfate proteoglycans (HSPGs). This was confirmed by SDS-PAGE. The CS/DS PGs in the cell layer of stem cells had an apparent M(r) of approximately > 200 kDa, and the HSPGs had an apparent M(r) of approximately 140-230 kDa. In contrast, the major PGs in the cell layer of neurons consisted primarily of HSPGs, with only a minor proportion of CS/DS PGs. Furthermore, both gel filtration chromatography and SDS-PAGE analysis revealed a larger HSPG in the cell layer of neurons (Kav = 0.3-0.6 on CL-4B following chondroitin ABC lyase digestion; M(r) 170 kDa- > 400 kDa on SDS-PAGE) in comparison to stem cells (Kav = 0.4-0.6 on CL-4B following chondroitin ABC lyase digestion; M(r) 140-230 kDa on SDS-PAGE). Likewise, the major PGs secreted into media of stem cells consisted almost exclusively of CS/DS PGs, with lesser amounts of HSPGs, whereas an increase in HSPGs in the media of neurons was apparent. Western, Northern, and immunocytochemical analysis demonstrated that mRNA transcript and protein levels for a specific HSPG (i.e., perlecan) markedly increased in cell layer following P19 neuronal differentiation. Perlecan core protein was identified by Western blot analysis using specific monoclonal and polyclonal antibodies, as a large HSPG with a core protein of apparent M(r) approximately 370-400 kDa, and was observed primarily in extracts from neurons. Northern blot analysis with a cDNA to perlecan revealed a significant (P < 0.01) 12.7-fold increase in expression of perlecan in neurons (day 9) in comparison to stem cells. The increase in perlecan message during P19 neuronal differentiation was concomitant with a significant (P < 0.01) 26.3-fold increase in message for beta-amyloid precursor protein (beta PP).(ABSTRACT TRUNCATED AT 400 WORDS)