Strange band pattern in Western Blot - (Sep/13/2014 )

I'm performing WB on cell lysates and I'm searching for Sirtuin 6. I'm using two different cell lines and I get the same result in both.
I purchased the Ab from Sigma and the band should be around 40 kb.
Instead what i get is this...

The first two bands are about 80-90 kb while the lower one is about 30-35.
Why do I get those two high bands (which are pretty dark)?
I use Bio Rad precast gels and I blot on PVDF membranes.

Titrate the antibody (range of different dilutions, starting well below where you are currently using it), also - are these cells supposed to be sirtuin positive? If they are unknowns then you need a known positive to test the antibody with.