How to select a cell type to study my gene - (Nov/09/2007 )

I'm studying the role of a transcriptional factor play in the breast cancers. I want to transfect the transcriptional factor to cells and don't know which cell type I should choose.Can anyone help me?
I want to do the following things with the transfected cells:

1, Chip on chip assay to find the promoter the transcriptional factor binds
2, DNA microarray to see what genes are upregulated or downregulated
3, Localization of the transcriptional facotr
4, transfect my gene to a breast cancer cell line to see if there are any phenotypes.

Should I use breast cancer cell lines or I can use 293T cells to do the above experiments( except 4 in which I will definitely use breast cancer cell line)?If I choose breast cancer cell line, should I choose a cell line that does't express the endogenous transcriptional factor or should I choose the cell line that express the endogenous transcriptional factor? I heard MCF7 is easy to do transfection, it express the endogenous transcriptional factor, can I use MCF-7?

As ur studies includes identification of the sites on promoter to which ur transcriptiona factor binds i think its good idea to start with breast cancer cell line which doesn't express the endogenous transcriptional factor.

Definitely use a breast cell line in my opinion. The importance of cell line is just so neglected in research. Isn't the reason there is such a thing as cell types because they are all different? So why would you use an embryonic kidney cell line when you are studying breast cancer? What does an embryonic kidney have to do with breast cancer? I've just never understood it. Any way, so there's my rant, keep it as relevant as possible - that's breast for me.